Timing advance configuration for multiple uplink component carriers

ABSTRACT

The invention relates methods for time aligning uplink transmissions by a mobile terminal in a mobile communication system, and to methods for performing a handover of a mobile terminal to a target aggregation access point. The invention is also providing apparatus and system for performing these methods, and computer readable media the instructions of which cause the apparatus and system to perform the methods described herein. In order to allow for aligning the timing of uplink transmissions on uplink component carriers, where different propagation delays are imposed on the transmissions on the uplink component carriers, the inventions suggests to time align the uplink component carriers based on a reference time alignment of a reference cell and a reception time difference or propagation delay difference between the downlink transmissions in the reference cell and the other radio cells, the uplink component carriers of which need to be time aligned.

FIELD OF THE INVENTION

The invention relates methods for time aligning uplink transmissions bya mobile terminal in a mobile communication system. The invention isalso providing apparatus and system for performing the methods describedherein, as well as computer readable media the instructions of whichcause the apparatus and system to perform the methods described herein.

TECHNICAL BACKGROUND

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving aradio-access technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support to the next decade. Theability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is to be finalized as Release 8 (LTE Rel. 8). TheLTE system represents efficient packet-based radio access and radioaccess networks that provide full IP-based functionalities with lowlatency and low cost. In LTE, scalable multiple transmission bandwidthsare specified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in orderto achieve flexible system deployment using a given spectrum. In thedownlink, Orthogonal Frequency Division Multiplexing (OFDM) based radioaccess was adopted because of its inherent immunity to multipathinterference (MPI) due to a low symbol rate, the use of a cyclic prefix(CP), and its affinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA) based radioaccess was adopted in the uplink, since provisioning of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmit power of the user equipment (UE).Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniques,and a highly efficient control signaling structure is achieved in LTERel. 8/9.

LTE Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2. TheE-UTRAN consists of eNodeB, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY),Medium Access Control (MAC), Radio Link Control (RLC), and Packet DataControl Protocol (PDCP) layers that include the functionality ofuser-plane header-compression and encryption. It also offers RadioResource Control (RRC) functionality corresponding to the control plane.It performs many functions including radio resource management,admission control, scheduling, enforcement of negotiated uplink Qualityof Service (QoS), cell information broadcast, ciphering/deciphering ofuser and control plane data, and compression/decompression ofdownlink/uplink user plane packet headers. The eNodeBs areinterconnected with each other by means of the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relation betweenMMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user datapackets, while also acting as the mobility anchor for the user planeduring inter-eNodeB handovers and as the anchor for mobility between LTEand other 3GPP technologies (terminating S4 interface and relaying thetraffic between 2G/3G systems and PDN GW). For idle state userequipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g. parameters of the IP bearerservice, network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at time of intra-LTEhandover involving Core Network (CN) node relocation. It is responsiblefor authenticating the user (by interacting with the HSS). TheNon-Access Stratum (NAS) signaling terminates at the MME and it is alsoresponsible for generation and allocation of temporary identities touser equipments. It checks the authorization of the user equipment tocamp on the service provider's Public Land Mobile Network (PLMN) andenforces user equipment roaming restrictions. The MME is the terminationpoint in the network for ciphering/integrity protection for NASsignaling and handles the security key management. Lawful interceptionof signaling is also supported by the MME. The MME also provides thecontrol plane function for mobility between LTE and 2G/3G accessnetworks with the S3 interface terminating at the MME from the SGSN. TheMME also terminates the S6a interface towards the home HSS for roaminguser equipments.

L1/2 Control Signalling

In order to inform the scheduled users about their allocation status,transport format and other data related information (e.g. HARQ) L1/L2control signaling needs to be transmitted on the downlink along with thedata. The control signaling needs to be multiplexed with the downlinkdata in a sub frame (assuming that the user allocation can change fromsub frame to sub frame). Here, it should be noted that user allocationmight also be performed on a TTI (Transmission Time Interval) basis,where the TTI length may be a multiple of the sub frames. The TTI lengthmay be fixed in a service area for all users, may be different fordifferent users, or may even by dynamic for each user. Generally, thenthe L1/2 control signaling needs only be transmitted once per TTI. TheL1/L2 control signalling is transmitted on the Physical Downlink ControlChannel (PDCCH). It should be noted that assignments for uplink datatransmissions, UL grants, are also transmitted on the PDCCH.

Generally, the information sent on the L1/L2 control signaling may beseparated into the following two categories:

-   -   Shared Control Information (SCI) carrying Cat 1 information. The        SCI part of the L1/L2 control signaling contains information        related to the resource allocation (indication). The SCI        typically contains the following information:        -   User identity, indicating the user which is allocated        -   RB allocation information, indicating the resources            (Resource Blocks, RBs) on which a user is allocated. Note,            that the number of RBs on which a user is allocated can be            dynamic.        -   Optional: Duration of assignment, if an assignment over            multiple sub frames (or TTIs) is possible    -   Depending on the setup of other channels and the setup of the        Dedicated Control Information (DCI), the SCI may additionally        contain information such as ACK/NACK for uplink transmission,        uplink scheduling information, information on the DCI (resource,        MCS, etc.).    -   Dedicated Control Information (DCI) carrying Cat 2/3 information    -   The DCI part of the L1/L2 control signaling contains information        related to the transmission format (Cat 2) of the data        transmitted to a scheduled user indicated by Cat 1. Moreover, in        case of application of (hybrid) ARQ it carries HARQ (Cat 3)        information. The DCI needs only to be decoded by the user        scheduled according to Cat 1. The DCI typically contains        information on:        -   Cat 2: Modulation scheme, transport block (payload) size (or            coding rate), MIMO related information, etc.        -   Cat 3: HARQ related information, e.g. hybrid ARQ process            number, redundancy version, retransmission sequence number

In the following the detailed L1/L2 control signalling informationsignalled for DL allocation respectively uplink assignments is describedin the following:

Downlink Data Transmission:

-   -   Along with the downlink packet data transmission, L1/L2 control        signaling is transmitted on a separate physical channel (PDCCH).        This L1/L2 control signaling typically contains information on:        -   The physical resource(s) on which the data is transmitted            (e.g. subcarriers or subcarrier blocks in case of OFDM,            codes in case of CDMA). This information allows the UE            (receiver) to identify the resources on which the data is            transmitted.        -   The transport Format, which is used for the transmission.            This can be the transport block size of the data (payload            size, information bits size), the MCS (Modulation and Coding            Scheme) level, the Spectral Efficiency, the code rate, etc.            . . . . This information (usually together with the resource            allocation) allows the UE (receiver) to identify the            information bit size, the modulation scheme and the code            rate in order to start the demodulation, the de rate            matching and the decoding process. In some cases the            modulation scheme maybe signaled explicitly.        -   Hybrid ARQ (HARQ) Information:            -   Process number: Allows the UE to identify the hybrid ARQ                process on which the data is mapped            -   Sequence number or new data indicator: Allows the UE to                identify if the transmission is a new packet or a                retransmitted packet            -   Redundancy and/or constellation version: Tells the UE,                which hybrid ARQ redundancy version is used (required                for de-rate matching) and/or which modulation                constellation version is used (required for                demodulation)        -   UE Identity (UE ID): Tells for which UE the L1/L2 control            signaling is intended for. In typical implementations this            information is used to mask the CRC of the L1/L2 control            signaling in order to prevent other UEs to read this            information.

Uplink Data Transmission:

-   -   To enable an uplink packet data transmission, L1/L2 control        signaling is transmitted on the downlink (PDCCH) to tell the UE        about the transmission details. This L1/L2 control signaling        typically contains information on:        -   The physical resource(s) on which the UE should transmit the            data (e.g. subcarriers or subcarrier blocks in case of OFDM,            codes in case of CDMA).        -   The transport Format, the UE should use for the            transmission. This can be the transport block size of the            data (payload size, information bits size), the MCS            (Modulation and Coding Scheme) level, the Spectral            Efficiency, the code rate, etc. This information (usually            together with the resource allocation) allows the UE            (transmitter) to pick the information bit size, the            modulation scheme and the code rate in order to start the            modulation, the rate matching and the encoding process. In            some cases the modulation scheme maybe signaled explicitly.        -   Hybrid ARQ information:            -   Process number: Tells the UE from which hybrid ARQ                process it should pick the data            -   Sequence number or new data indicator: Tells the UE to                transmit a new packet or to retransmit a packet            -   Redundancy and/or constellation version: Tells the UE,                which hybrid ARQ redundancy version to use (required for                rate matching) and/or which modulation constellation                version to use (required for modulation)        -   UE Identity (UE ID): Tells which UE should transmit data. In            typical implementations this information is used to mask the            CRC of the L1/L2 control signaling in order to prevent other            UEs to read this information.

There are several different flavors how to exactly transmit theinformation pieces mentioned above. Moreover, the L1/L2 controlinformation may also contain additional information or may omit some ofthe information. E.g.:

-   -   HARQ process number may not be needed in case of a synchronous        HARQ protocol    -   A redundancy and/or constellation version may not be needed if        Chase Combining is used (always the same redundancy and/or        constellation version) or if the sequence of redundancy and/or        constellation versions is pre defined.    -   Power control information may be additionally included in the        control signaling    -   MIMO related control information, such as e.g. precoding, may be        additionally included in the control signaling.    -   In case of multi-codeword MIMO transmission transport format        and/or HARQ information for multiple code words may be included

For uplink resource assignments (PUSCH) signalled on PDCCH in LTE, theL1/L2 control information does not contain a HARQ process number, sincea synchronous HARQ protocol is employed for LTE uplink. The HARQ processto be used for an uplink transmission is given by the timing.Furthermore it should be noted that the redundancy version (RV)information is jointly encoded with the transport format information,i.e. the RV info is embedded in the transport format (TF) field. The TFrespectively MCS field has for example a size of 5 bits, whichcorresponds to 32 entries. 3 TF/MCS table entries are reserved forindicating RVs 1, 2 or 3. The remaining MCS table entries are used tosignal the MCS level (TBS) implicitly indicating RV0. The size of theCRC field of the PDCCH is 16 bits. Further detailed information on thecontrol information for uplink resource allocation on PUSCH can be foundin TS36.212 section 5.3.3 and TS36.213 section 8.6.

For downlink assignments (PDCCH) signalled on PDCCH in LTE theRedundancy Version (RV) is signalled separately in a two-bit field.Furthermore the modulation order information is jointly encoded with thetransport format information. Similar to the uplink case there is 5 bitMCS field signalled on PDCCH. 3 of the entries are reserved to signal anexplicit modulation order, providing no Transport format (Transportblock) info. For the remaining 29 entries modulation order and Transportblock size info are signalled. Further detailed information on thecontrol information for uplink resource allocation on PUSCH can be foundin TS36.212 section 5.3.3 and TS36.213 section 7.1.7

Component Carrier Structure in LTE (Release 8)

The downlink component carrier of a 3GPP LTE (Release 8) is subdividedin the time-frequency domain in so-called sub-frames. In 3GPP LTE(Release 8) each sub-frame is divided into two downlink slots as shownin FIG. 3, wherein the first downlink slot comprises the control channelregion (PDCCH region) within the first OFDM symbols. Each sub-frameconsists of a give number of OFDM symbols in the time domain (12 or 14OFDM symbols in 3GPP LTE (Release 8)), wherein each of OFDM symbol spansover the entire bandwidth of the component carrier. The OFDM symbolsthus each consists of a number of modulation symbols transmitted onrespective N_(RB) ^(DL)×N_(SC) ^(RB) subcarriers as also shown in FIG.4.

Assuming a multi-carrier communication system, e.g. employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block is defined as N_(symb) ^(DL) consecutive OFDMsymbols in the time domain and N_(ac) ^(RB) consecutive subcarriers inthe frequency domain as exemplified in FIG. 4. In 3GPP LTE (Release 8),a physical resource block thus consists of N_(symb) ^(DL)×N_(SC) ^(RB)resource elements, corresponding to one slot in the time domain and 180kHz in the frequency domain (for further details on the downlinkresource grid, see for example 3GPP TS 36.211, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, version 8.9.0 or 9.0.0, section 6.2, available athttp://www.3gpp.org and incorporated herein by reference).

The term “component carrier” refers to a combination of several resourceblocks. In future releases of LTE, the term “component carrier” is nolonger used; instead, the terminology is changed to “cell”, which refersto a combination of downlink and optionally uplink resources. Thelinking between the carrier frequency of the downlink resources and thecarrier frequency of the uplink resources is indicated in the systeminformation transmitted on the downlink resources.

Further Advancements for LTE (LTE-A)

The frequency spectrum for IMT-Advanced was decided at the WorldRadiocommunication Conference 2007 (WRC-07). Although the overallfrequency spectrum for IMT-Advanced was decided, the actual availablefrequency bandwidth is different according to each region or country.Following the decision on the available frequency spectrum outline,however, standardization of a radio interface started in the 3rdGeneration Partnership Project (3GPP). At the 3GPP TSG RAN #39 meeting,the Study Item description on “Further Advancements for E-UTRA(LTE-Advanced)” was approved. The study item covers technologycomponents to be considered for the evolution of E-UTRA, e.g. to fulfillthe requirements on IMT-Advanced. Two major technology components whichare currently under consideration for LTE-A are described in thefollowing.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers (componentcarriers) are aggregated in order to support wider transmissionbandwidths up to 100 MHz. Several cells in the LTE system are aggregatedinto one wider channel in the LTE-Advanced system which is wide enoughfor 100 MHz even though these cells in LTE are in different frequencybands.

All component carriers can be configured to be LTE Rel. 8/9 compatible,at least when the aggregated numbers of component carriers in the uplinkand the downlink are the same. Not all component carriers aggregated bya user equipment may necessarily be Rel. 8/9 compatible. Existingmechanism (e.g. barring) may be used to avoid Rel-8/9 user equipments tocamp on a component carrier.

A user equipment may simultaneously receive or transmit one or multiplecomponent carriers (corresponding to multiple serving cells) dependingon its capabilities. A LTE-A Rel. 10 user equipment with receptionand/or transmission capabilities for carrier aggregation cansimultaneously receive and/or transmit on multiple serving cells,whereas an LTE Rel. 8/9 user equipment can receive and transmit on asingle serving cell only, provided that the structure of the componentcarrier follows the Rel. 8/9 specifications.

Carrier aggregation is supported for both contiguous and non-contiguouscomponent carriers with each component carrier limited to a maximum of110 Resource Blocks in the frequency domain using the Rel. 8/9numerology. It is possible to configure a user equipment to aggregate adifferent number of component carriers originating from the same eNodeBand of possibly different bandwidths in the uplink and the downlink:

-   -   The number of downlink component carriers that can be configured        depends on the downlink aggregation capability of the user        equipment;    -   The number of uplink component carriers that can be configured        depends on the uplink aggregation capability of the user        equipment;    -   It is not possible to configure a user equipment with more        uplink component carriers than downlink component carriers;    -   In typical TDD deployments, the number of component carriers and        the bandwidth of each component carrier in uplink and downlink        is the same.

Component carriers originating from the same eNodeB need not to providethe same coverage.

The spacing between centre frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of Rel. 8/9 and at thesame time preserve orthogonality of the subcarriers with 15 kHz spacing.Depending on the aggregation scenario, the n×300 kHz spacing can befacilitated by insertion of a low number of unused subcarriers betweencontiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO—Single User Multiple Input Multiple Output—foruplink) at most one transport block per component carrier. A transportblock and its potential HARQ retransmissions need to be mapped on thesame component carrier. The Layer 2 structure with activated carrieraggregation is shown in FIG. 5 and FIG. 6 for the downlink and uplinkrespectively.

When carrier aggregation is configured, the user equipment only has oneRRC connection with the network. At RRC connectionestablishment/re-establishment, one serving cell provides the securityinput (one ECGI, one PCI and one ARFCN) and the non-access stratummobility information (e.g. TAI) similarly as in LTE Rel. 8/9. After RRCconnection establishment/re-establishment, the component carriercorresponding to that cell is referred to as the downlink Primary Cell(PCell). There is always one and only one downlink PCell (DL PCell) andone uplink PCell (UL PCell) configured per user equipment in connectedmode. In the downlink, the carrier corresponding to the PCell is theDownlink Primary Component Carrier (DL PCC), while in the uplink it isthe Uplink Primary Component Carrier (UL PCC).

Depending on the user equipment's capabilities, Secondary Cells (SCells)can be configured to form a set of serving cells, together with thePCell. Therefore, the configured set of serving cells for a userequipment always consists of one PCell and one or more SCells. Thecharacteristics of the downlink and uplink PCell and SCells are

-   -   The uplink PCell is used for transmission of Layer 1 uplink        control information (PUCCH)    -   Unlike SCells, the downlink PCell cannot be de-activated    -   Re-establishment is triggered when the downlink PCell        experiences Rayleigh fading (RLF), not when downlink SCells        experience RLF    -   For each SCell the usage of uplink resources by the UE in        addition to the downlink ones is configurable (the number of DL        SCCs configured is therefore always larger or equal to the        number of UL SCells and no SCell can be configured for usage of        uplink resources only)    -   From a UE viewpoint, each uplink resource only belongs to one        serving cell    -   PCell can only be changed with handover procedure (i.e. with        security key change and RACH procedure)    -   The number of serving cells that can be configured depends on        the aggregation capability of the UE    -   Non-access stratum information is taken from the downlink PCell.

The reconfiguration, addition and removal of SCells can be performed byRRC. At intra-LTE handover, RRC can also add, remove, or reconfigureSCells for usage with the target PCell. When adding a new SCell,dedicated RRC signaling is used for sending all required systeminformation of the SCell, i.e. while in connected mode, user equipmentsneed not acquire broadcast system information directly from the SCells.

When carrier aggregation is configured, a user equipment may bescheduled over multiple component carriers simultaneously, but at mostone random access procedure should be ongoing at any time. Cross-carrierscheduling allows the Physical Downlink Control Channel (PDCCH) of acomponent carrier to schedule resources on another component carrier.For this purpose a component carrier identification field (CIF) isintroduced in the respective Downlink Control Information (DCI) formats.A linking between uplink and downlink component carriers allowsidentifying the uplink component carrier for which the grant applieswhen there is no-cross-carrier scheduling. The linkage of downlinkcomponent carriers to uplink component carriers does not necessarilyneed to be one to one. In other words, more than one downlink componentcarrier can link to the same uplink component carrier. At the same time,a downlink component carrier can only link to one uplink componentcarrier.

Activation/Deactivation of SCells

To enable reasonable UE battery consumption when CA is configured, anactivation/deactivation mechanism of SCells is supported (i.e.activation/deactivation does not apply to PCell). When an SCell isdeactivated, the UE does not need to receive the corresponding PDCCH orPDSCH, cannot transmit in the corresponding uplink, nor is it requiredto perform CQI measurements. Conversely, when an SCell is active, the UEshall receive PDSCH and PDCCH (if the UE is configured to monitor PDCCHfrom this SCell), and is expected to be able to perform CQImeasurements.

The activation/deactivation mechanism is based on the combination of aMAC control element and deactivation timers. The MAC control elementcarries a bitmap for the activation and deactivation of SCells: a bitset to 1 denotes activation of the corresponding SCell, while a bit setto 0 denotes deactivation. With the bitmap, SCells can be activated anddeactivated individually, and a single activation/deactivation commandcan activate/deactivate a subset of the SCells. The correspondingactivation/deactivation MAC CE is shown in FIG. 20. It should be noted,that even though there is a maximum of 4 Scells a UE can aggregate, theMAC CE contains 7 entries, each of them corresponding to an SCellconfigured with SCellIndex i.

One deactivation timer is maintained per SCell but one common value isconfigured per UE by RRC. At reconfiguration without mobility controlinformation:

-   -   SCells added to the set of serving cells are initially        “deactivated”;    -   SCells which remain in the set of serving cells (either        unchanged or reconfigured) do not change their activation status        (“activated” or “deactivated”).        At reconfiguration with mobility control information (i.e.        handover):    -   SCells are “deactivated”.        Uplink Access Scheme for LTE

For Uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. The main reason for thepreference for single-carrier transmission is the lower peak-to-averagepower ratio (PAPR), compared to multi-carrier signals (OFDMA), and thecorresponding improved power-amplifier efficiency and assumed improvedcoverage (higher data rates for a given terminal peak power). Duringeach time interval, Node B assigns users a unique time/frequencyresource for transmitting user data thereby ensuring intra-cellorthogonality. An orthogonal access in the uplink promises increasedspectral efficiency by eliminating intra-cell interference. Interferencedue to multipath propagation is handled at the base station (Node B),aided by insertion of a cyclic prefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BWgrant during one time interval, e.g. asub-frame of 0.5 ms, onto which coded information bits are mapped. Itshould be noted that a sub-frame, also referred to as transmission timeinterval (TTI), is the smallest time interval for user datatransmission. It is however possible to assign a frequency resourceBWgrant over a longer time period than one TTI to a user byconcatenation of sub-frames.

Uplink Scheduling Scheme for LTE

The uplink scheme allows for both scheduled access, i.e. controlled byeNB, and contention-based access.

In case of scheduled access the UE is allocated a certain frequencyresource for a certain time (i.e. a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access. Within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is for example the randomaccess, i.e. when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines

-   -   which UE(s) that is (are) allowed to transmit,    -   which physical channel resources (frequency),    -   Transport format (Modulation Coding Scheme (MCS)) to be used by        the mobile terminal for transmission

The allocation information is signalled to the UE via a schedulinggrant, sent on the L1/L2 control channel. For simplicity reasons thischannel is called uplink grant channel in the following. A schedulinggrant message contains at least information which part of the frequencyband the UE is allowed to use, the validity period of the grant, and thetransport format the UE has to use for the upcoming uplink transmission.The shortest validity period is one sub-frame. Additional informationmay also be included in the grant message, depending on the selectedscheme. Only “per UE” grants are used to grant the right to transmit onthe UL-SCH (i.e. there are no “per UE per RB” grants). Therefore the UEneeds to distribute the allocated resources among the radio bearersaccording to some rules, which will be explained in detail in the nextsection. Unlike in HSUPA there is no UE based transport formatselection. The eNB decides the transport format based on someinformation, e.g. reported scheduling information and QoS info, and UEhas to follow the selected transport format. In HSUPA Node B assigns themaximum uplink resource and UE selects accordingly the actual transportformat for the data transmissions.

Since the scheduling of radio resources is the most important functionin a shared channel access network for determining Quality of service,there are a number of requirements that should be fulfilled by the ULscheduling scheme for LTE in order to allow for an efficient QoSmanagement.

-   -   Starvation of low priority services should be avoided    -   Clear QoS differentiation for radio bearers/services should be        supported by the scheduling scheme    -   The UL reporting should allow fine granular buffer reports (e.g.        per radio bearer or per radio bearer group) in order to allow        the eNB scheduler to identify for which Radio Bearer/service        data is to be sent.    -   It should be possible to make clear QoS differentiation between        services of different users    -   It should be possible to provide a minimum bit rate per radio        bearer

As can be seen from above list one essential aspect of the LTEscheduling scheme is to provide mechanisms with which the operator cancontrol the partitioning of its aggregated cell capacity between theradio bearers of the different QoS classes. The QoS class of a radiobearer is identified by the QoS profile of the corresponding SAE bearersignalled from AGW to eNB as described before. An operator can thenallocate a certain amount of its aggregated cell capacity to theaggregated traffic associated with radio bearers of a certain QoS class.The main goal of employing this class-based approach is to be able todifferentiate the treatment of packets depending on the QoS class theybelong to.

Uplink Power Control

Uplink transmission power control in a mobile communication systemserves an important purpose: it balances the need for sufficienttransmitted energy per bit to achieve the required Quality-of-Service(QoS), against the needs to minimize interference to other users of thesystem and to maximize the battery life of the mobile terminal. Inachieving this purpose, the role of the Power Control (PC) becomesdecisive to provide the required SINR while controlling at the same timethe interference caused to neighbouring cells. The idea of classic PCschemes in uplink is that all users are received with the same SINR,which is known as full compensation. As an alternative, 3GPP has adoptedfor LTE the use of Fractional Power Control (FPC). This newfunctionality makes users with a higher path-loss operate at a lowerSINR requirement so that they will more likely generate lessinterference to neighbouring cells.

Detailed power control formulae are specified in LTE for the PhysicalUplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH)and the Sounding Reference Signals (SRSs) (section 5.1 in TS36.213). Theformula for each of these uplink signals follows the same basicprinciples; in all cases they can be considered as a summation of twomain terms: a basic open-loop operating point derived from static orsemi-static parameters signalled by the eNodeB, and a dynamic offsetupdated from subframe to subframe.

The basic open-loop operating point for the transmit power per resourceblock depends on a number of factors including the inter-cellinterference and cell load. It can be further broken down into twocomponents, a semi-static base level P0, further comprised of a commonpower level for all UEs in the cell (measured in dBm) and a UE-specificoffset, and an open-loop path-loss compensation component. The dynamicoffset part of the power per resource block can also be further brokendown into two components, a component dependent on the MCS and explicitTransmitter Power Control (TPC) commands.

The MCS-dependent component (referred to in the LTE specifications asΔ_(TF), where TF stands for ‘Transport Format’) allows the transmittedpower per RB to be adapted according to the transmitted information datarate.

The other component of the dynamic offset is the UE-specific TPCcommands. These can operate in two different modes: accumulative TPCcommands (available for PUSCH, PUCCH and SRS) and absolute TPC commands(available for PUSCH only). For the PUSCH, the switch between these twomodes is configured semi-statically for each UE by RRC signalling—i.e.the mode cannot be changed dynamically. With the accumulative TPCcommands, each TPC command signals a power step relative to the previouslevel.

The formula below shows the UE transmit power, expressed in dBm, forPUSCH:P=min└P _(MAX),10·log₁₀ M+P ₀ _(_) _(PUSCH)+α·PL+Δ_(MCS)+ƒ(Δ_(i))┘dBm]

-   -   PMAX is the maximum UE power which depends on the UE class.    -   M is the number of allocated physical resource blocks (PRBs).    -   PL is the UE path loss derived at the UE based on RSRP        measurement and signalled RS eNode-B transmission power.    -   Δ_(MCS) is an MCS-dependent power offset set by the eNB.    -   P₀ _(_) _(PUSCH) is a UE-specific parameter (partially        broadcasted and partially signalled using RRC).    -   α is cell-specific parameter (broadcasted on BCH).    -   Δ_(i) are closed loop PC commands signalled from the eNode-B to        the UE    -   function f ( ) indicates whether closed loop commands are        relative accumulative or absolute. f ( ) is signalled to the UE        via higher layers.        Uplink Power Control for Carrier Aggregation

One main point of UL Power control for LTE-Advance is that a componentcarrier specific UL power control is supported, i.e. there will be oneindependent power control loop for each UL component carrier configuredfor the UE. Furthermore power headroom is reported per componentcarrier.

In Rel-10 within the scope of carrier aggregation there are two maximumpower limits, a maximum total UE transmit power and a CC-specificmaximum transmit power. RAN1 agreed at the RAN1#60bis meeting that apower headroom report, which is reported per CC, accounts for themaximum power reduction (MPR). In other words the power reductionapplied by the UE is taken into account in the CC-specific maximumtransmission power P_(CMAX,c) (c denotes the component carrier).

Different to Rel-8/9, for LTE-A the UE has also to cope withsimultaneous PUSCH-PUCCH transmission, multi-cluster scheduling andsimultaneous transmission on multiple CCs, which requires larger MPRvalues and also causes a larger variation of the applied MPR valuescompared to Rel-8/9.

It should be noted that the eNB does not have knowledge of the powerreduction applied by the UE on each CC, since the actual power reductiondepends on the type of allocation, the standardized MPR value and alsoon the UE implementation. Therefore eNB doesn't know the CC-specificmaximum transmission power relative to which the UE calculates the PHR.

In Rel-8/9 for example UE's maximum transmit power Pcmax can be withinsome certain range as described above.P _(CMAX) _(_) _(L) ≦P _(CMAX) ≦P _(CMAX) _(_) _(H)

Due to the fact that the power reduction applied by the UE to themaximum transmit power of a CC is not known by eNB it was agreed tointroduce in Rel-10 a new power headroom MAC control element, which isalso referred to as extended power headroom MAC control element. Themain difference to the Rel-8/9 PHR MAC CE format, is that it includes aRel-8/9 power headroom value for each activated UL CC and is hence ofvariable size. Furthermore it not only reports the power headroom valuefor a CC but also the corresponding Pcmax,c (maximum transmit power ofCC with the index c) value. In order to account for simultaneousPUSCH-PUCCH transmissions, UE reports for PCell the Rel-8/9 powerheadroom value which is related to PUSCH only transmissions (referred totype 1 power headroom) and if the UE is configured for simultaneousPUSCH-PUCCH transmission, a further Power headroom value, whichconsiders PUCCH and PUSCH transmissions, also referred to as type 2power headroom (see FIG. 21). Further details of the extended powerheadroom MAC Control element can be found in section 6.1.3.6a ofTS36.321.

If the total transmit power of the UE, i.e. sum of transmission power onall CCs, would exceed the maximum UE transmit power {circumflex over(P)}_(CMAX)(i), the UE needs to scale down uplink transmission power onPUSCH/PUCCH. There are certain rules for the prioritization of theuplink channels during power scaling defined. Basically controlinformation transmitted on the PUCCH has the highest priority, i.e.PUSCH transmissions are scaled down first before PUCCH transmissionpower is reduced. This can be also expressed by the following conditionwhich needs to be fulfilled:

${\sum\limits_{c}\;{{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}} \leq \left( {{{\hat{P}}_{CMAX}(i)} - {{\hat{P}}_{PUCCH}(i)}} \right)$where {circumflex over (P)}_(PUCCH)(i) is the linear value ofP_(PUCCH)(i) (PUCCH transmission power in subframe i), {circumflex over(P)}_(PUSCH,c)(i) is the linear value of P_(PUSCH,c)(i) (PUSCHtransmission power on carrier c in subframe i), {circumflex over(P)}_(CMAX)(i) is the linear value of the UE total configured maximumoutput power P_(CMAX) in subframe i and w(i) is a scaling factor of{circumflex over (P)}_(PUSCH,c)(i) for serving cell c where 0≦w(i)≦1. Incase there is no PUCCH transmission in subframe i, {circumflex over(P)}_(PUCCH)(i)=0.

For the case that the UE has PUSCH transmission with Uplink controlinformation (UCI) on serving cell j and PUSCH without UCI in any of theremaining serving cells, and the total transmit power of the UE wouldexceed {circumflex over (P)}_(CMAX)(i), the UE scales {circumflex over(P)}_(PUSCH,c)(i) for the serving cells without UCI in subframe/suchthat the condition

${\sum\limits_{c \neq j}\;{{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}} \leq \left( {{{\hat{P}}_{CMAX}(i)} - {{\hat{P}}_{{PUSCH},j}(i)}} \right)$is satisfied where {circumflex over (P)}_(PUSCH,j)(i) is the PUSCHtransmit power for the cell with UCI and w(i) is a scaling factor of{circumflex over (P)}_(PUSCH,c)(i) for serving cell c without UCI. Inthis case, no power scaling is applied to {circumflex over(P)}_(PUSCH,j)(i) unless

${\sum\limits_{c \neq j}\;{{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}} = 0$and the total transmit power of the UE still would exceed {circumflexover (P)}_(CMAX)(i). Note that w(i) values are the same across servingcells when w(i)>0 but for certain serving cells w(i) may be zero.

If the UE has simultaneous PUCCH and PUSCH transmission with UCI onserving cell j and PUSCH transmission without UCI in any of theremaining serving cells, and the total transmit power of the UE wouldexceed {circumflex over (P)}_(CMAX)(i), the UE obtains {circumflex over(P)}_(PUSCH,c)(i) according to

P̂_(PUSCH, j)(i) = min (P̂_(PUSCH, j)(i), (P̂_(CMAX)(i) − P̂_(PUCCH)(i)))  and${\sum\limits_{c \neq j}\;{{w(i)} \cdot {{\hat{P}}_{{PUSCH},c}(i)}}} \leq \left( {{{\hat{P}}_{CMAX}(i)} - {{\hat{P}}_{PUCCH}(i)} - {{\hat{P}}_{{PUSCH},j}(i)}} \right)$Timing Advance

For the uplink transmission scheme of 3GPP LTE single-carrier frequencydivision multiple access (SC-FDMA) was chosen to achieve an orthogonalmultiple-access in time and frequency between the different userequipments transmitting in the uplink.

Uplink orthogonality is maintained by ensuring that the transmissionsfrom different user equipments in a cell are time-aligned at thereceiver of the eNodeB. This avoids intra-cell interference occurring,both between user equipments assigned to transmit in consecutivesub-frames and between user equipments transmitting on adjacentsubcarriers. Time alignment of the uplink transmissions is achieved byapplying a timing advance at the user equipment's transmitter, relativeto the received downlink timing as exemplified in FIG. 9. The main roleof this is to counteract differing propagation delays between differentuser equipments.

Initial Timing Advance Procedure

When user equipment is synchronized to the downlink transmissionsreceived from eNodeB, the initial timing advance is set by means of therandom access procedure as described below. The user equipment transmitsa random access preamble based on which the eNodeB can estimate theuplink timing. The eNodeB responds with an 11-bit initial timing advancecommand contained within the Random Access Response (RAR) message. Thisallows the timing advance to be configured by the eNodeB with agranularity of 0.52 μs from 0 up to a maximum of 0.67 ms.

Additional information on the control of the uplink timing and timingadvance on 3GPP LTE (Release 8/9) can be found in chapter 20.2 ofStefania Sesia, Issam Toufik and Matthew Baker, “LTE The UMTS Long TermEvolution: From Theory to Practice”, John Wiley & Sons, Ltd. 2009, whichis incorporated herein by reference.

Updates of the Timing Advance

Once the timing advance has been first set for each user equipment, thetiming advance is updated from time to time to counteract changes in thearrival time of the uplink signals at the eNodeB. In deriving the timingadvance update commands, the eNodeB may measure any uplink signal whichis useful. The details of the uplink timing measurements at the eNodeBare not specified, but left to the implementation of the eNodeB.

The timing advance update commands are generated at the Medium AccessControl (MAC) layer in the eNodeB and transmitted to the user equipmentas MAC control elements which may be multiplexed together with data onthe Physical Downlink Shared Channel (PDSCH). Like the initial timingadvance command in the response to the Random Access Channel (RACH)preamble, the update commands have a granularity of 0.52 μs. The rangeof the update commands is ±16 μs, allowing a step change in uplinktiming equivalent to the length of the extended cyclic prefix. Theywould typically not be sent more frequently than about every 2 seconds.In practice, fast updates are unlikely to be necessary, as even for auser equipment moving at 500 km/h the change in round-trip path lengthis not more than 278 m/s, corresponding to a change in round-trip timeof 0.93 μs/s.

The eNodeB balances the overhead of sending regular timing updatecommands to all the UEs in the cell against a UE's ability to transmitquickly when data arrives in its transmit buffer. The eNodeB thereforeconfigures a timer for each user equipment, which the user equipmentrestarts each time a timing advance update is received. In case the userequipment does not receive another timing advance update before thetimer expires, it must then consider that it has lost uplinksynchronization (see also section 5.2 of 3GPP TS 36.321, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC)protocol specification”, version 8.9.0, available at http://www.3gpp.organd incorporated herein by reference).

In such a case, in order to avoid the risk of generating interference touplink transmissions from other user equipments, the UE is not permittedto make another uplink transmission of any sort and needs to revert tothe initial timing alignment procedure in order to restore the uplinktiming.

Upon reception of a timing advance command, the user equipment shalladjust its uplink transmission timing for PUCCH/PUSCH/SRS of the primarycell. The timing advance command indicates the change of the uplinktiming relative to the current uplink timing as multiples of 16 T_(s).

Random Access Procedure

A mobile terminal in LTE can only be scheduled for uplink transmission,if its uplink transmission is time synchronized. Therefore the RandomAccess (RACH) procedure plays an important role as an interface betweennon-synchronized mobile terminals (UEs) and the orthogonal transmissionof the uplink radio access.

Essentially the Random Access in LTE is used to achieve uplink timesynchronization for a user equipment which either has not yet acquired,or has lost, its uplink synchronization. Once a user equipment hasachieved uplink synchronization, the eNodeB can schedule uplinktransmission resources for it. The following scenarios are thereforerelevant for random access:

-   -   A user equipment in RRC_CONNECTED state, but not        uplink-synchronized, wishing to send new uplink data or control        information    -   A user equipment in RRC_CONNECTED state, but not        uplink-synchronized, required to receive downlink data, and        therefore to transmit corresponding HARQ feedback, i.e.        ACK/NACK, in the uplink. This scenario is also referred to as        Downlink data arrival    -   A user equipment in RRC_CONNECTED state, handing over from its        current serving cell to a new target cell; in order to achieve        uplink time-synchronization in the target cell, Random Access        procedure is performed    -   A transition from RRC_IDLE state to RRC_CONNECTED, for example        for initial access or tracking area updates    -   Recovering from radio link failure, i.e. RRC connection        re-establishment

There is one more additional case, where user equipment performs randomaccess procedure, even though user equipment is time-synchronized. Inthis scenario the user equipment uses the random access procedure inorder to send a scheduling request, i.e. uplink buffer status report, toits eNodeB, in case it does not have any other uplink resource allocatedin which to send the scheduling request, i.e. dedicated schedulingrequest (D-SR) channel is not configured.

LTE offers two types of random access procedures allowing access to beeither contention based, i.e. implying an inherent risk of collision, orcontention-free (non-contention based). It should be noted thatcontention-based random access can be applied for all six scenarioslisted above, whereas a non-contention based random access procedure canonly be applied for the downlink data arrival and handover scenario.

In the following the contention based random access procedure is beingdescribed in more detail with respect to FIG. 7. A detailed descriptionof the random access procedure can be also found in 3GPP 36.321, section5.1.

FIG. 7 shows the contention based RACH procedure of LTE. This procedureconsists of four “steps”. First, the user equipment transmits 701 arandom access preamble on the Physical Random Access Channel (PRACH) tothe eNodeB. The preamble is selected by user equipment from the set ofavailable random access preambles reserved by eNodeB for contentionbased access. In LTE, there are 64 preambles per cell which can be usedfor contention-free as well as contention based random access. The setof contention based preambles can be further subdivided into two groups,so that the choice of preamble can carry one bit of information toindicate information relating to the amount of transmission resourcesneeded for the first scheduled transmission, which is referred to asmsg3 in TS36.321 (see step 703). The system information broadcasted inthe cell contain the information which signatures (preambles) are ineach of the two subgroups as well as the meaning of each subgroup. Theuser equipment randomly selects one preamble from the subgroupcorresponding to the size of transmission resource needed for message 3transmission.

After eNodeB has detected a RACH preamble, it sends 702 a Random AccessResponse (RAR) message on the PDSCH (Physical Downlink Shared Channel)addressed on the PDCCH with the (Random Access) RA-RNTI identifying thetime-frequency slot in which the preamble was detected. If multiple userequipments transmitted the same RACH preamble in the same PRACHresource, which is also referred to as collision, they would receive thesame random access response.

The RAR message conveys the detected RACH preamble, a timing alignmentcommand (TA command) for synchronization of subsequent uplinktransmissions, an initial uplink resource assignment (grant) for thetransmission of the first scheduled transmission (see step 703) and anassignment of a Temporary Cell Radio Network Temporary Identifier(T-CRNTI). This T-CRNTI is used by eNodeB in order to address themobile(s) whose RACH preamble were detected until RACH procedure isfinished, since the “real” identity of the mobile is at this point notyet known by eNodeB.

Furthermore the RAR message can also contain a so-called back-offindicator, which the eNodeB can set to instruct the user equipment toback off for a period of time before retrying a random access attempt.The user equipment monitors the PDCCH for reception of random accessresponse within a given time window, which is configured by the eNodeB.In case user equipment doesn't receive a random access response withinthe configured time window, it retransmits the preamble at the nextPRACH opportunity considering a potentially back off period.

In response to the RAR message received from the eNodeB, the userequipment transmits 703 the first scheduled uplink transmission on theresources assigned by the grant within the random access response. Thisscheduled uplink transmission conveys the actual random access proceduremessage like for example RRC connection request, tracking area update orbuffer status report. Furthermore it includes either the C-RNTI for userequipments in RRC_CONNECTED mode or the unique 48-bit user equipmentidentity if the user equipments are in RRC_IDLE mode. In case of apreamble collision having occurred in step 701, i.e. multiple userequipments have sent the same preamble on the same PRACH resource, thecolliding user equipments will receive the same T-CRNTI within therandom access response and will also collide in the same uplinkresources when transmitting 703 their scheduled transmission. This mayresult in interference that no transmission from a colliding userequipment can be decoded at the eNodeB, and the user equipments willrestart the random access procedure after having reached maximum numberof retransmission for their scheduled transmission. In case thescheduled transmission from one user equipment is successfully decodedby eNodeB, the contention remains unsolved for the other userequipments.

For resolution of this type of contention, the eNode B sends 704 acontention resolution message addressed to the C-RNTI or TemporaryC-RNTI, and, in the latter case, echoes the 48-bit user equipmentidentity contained the scheduled transmission of step 703. It supportsHARQ. In case of collision followed by a successful decoding of themessage sent in step 703, the HARQ feedback (ACK) is only transmitted bythe user equipment which detects its own identity, either C-RNTI orunique user equipment ID. Other UEs understand that there was acollision at step 1 and can quickly exit the current RACH procedure andstart another one.

FIG. 8 is illustrating the contention-free random access procedure of3GPP LTE Rel. 8/9. In comparison to the contention based random accessprocedure, the contention-free random access procedure is simplified.The eNodeB provides 801 the user equipment with the preamble to use forrandom access so that there is no risk of collisions, i.e. multiple userequipment transmitting the same preamble. Accordingly, the userequipment is sending 802 the preamble which was signaled by eNodeB inthe uplink on a PRACH resource. Since the case that multiple UEs aresending the same preamble is avoided for a contention-free randomaccess, no contention resolution is necessary, which in turn impliesthat step 704 of the contention based procedure shown in FIG. 7 can beomitted. Essentially a contention-free random access procedure isfinished after having successfully received the random access response.

When carrier aggregation is configured, the first three steps of thecontention-based random access procedure occur on the PCell, whilecontention resolution (step 704) can be cross-scheduled by the PCell.

The initial preamble transmission power setting is based on an open-loopestimation with full compensation of the path loss. This is designed toensure that the received power of the preambles is independent of thepath-loss.

The eNB may also configure an additional power offset, depending forexample on the desired received SINR, the measured uplink interferenceand noise level in the time-frequency slots allocated to RACH preambles,and possibly on the preamble format. Furthermore, the eNB may configurepreamble power ramping so that the transmission for each retransmittedpreamble, i.e. in case the PRACH transmission attempt was notsuccessfully, is increased by a fixed step.

The PRACH power is determined by UE through evaluation ofPPRACH=min{P _(CMAX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PL_(C)}[dBm],where P_(CMAX,c)(i) is the configured maximum UE transmit power forsubframe i of the primary cell and PL_(C) is the downlink pathlossestimate calculated in the UE for the primary cell.PREAMBLE_RECEIVED_TARGET_POWER is set to:preambleInitialReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_TRANSMISSION_COUNTER−1)*powerRampingStep.Timing Advance and Component Carrier Aggregation in the Uplink

In currents specifications of the 3GPP standards the user equipment onlymaintains one timing advance value and applies this to uplinktransmissions on all aggregated component carriers. At the moment,aggregation of cells within the same frequency band is supported, socalled intra-frequency carrier aggregation. In particular, uplink timingsynchronization is performed for PCell, e.g. by RACH procedure on PCell,and then the user equipment uses the same uplink timing for uplinktransmissions on aggregated SCells. A single timing advance for allaggregated uplink component carriers is regarded as sufficient, sincecurrent specifications up to 3GPP LTE-A Rel. 10 support only carrieraggregation of carriers from the same frequency band.

However, in the future, e.g. future Release 11, it will be possible toaggregate uplink component carriers from different frequency bands, inwhich case they can experience different interference and coveragecharacteristics. Assuming uplink component carriers on widely separatedfrequency bands, uplink transmissions using the uplink componentcarriers may be subject to different transmission channel effects. Inother words, since transmission channels have to be assumed frequencyselective, uplink component carriers on widely separated frequency bandsmay be differently affected by scattering, multipath propagation andchannel fading. Accordingly, the aggregation of uplink componentcarriers from different frequency bands has to compensate for differentpropagation delays on the frequency bands.

Furthermore the deployment of technologies like Remote Radio Heads (RRH)as shown for example in FIG. 13 or Frequency Selective Repeaters (FSR)as shown for example in FIG. 14 will also cause different interferenceand propagation scenarios for the aggregated component carriers. Forinstance, FIG. 14 illustrates how the FSR relays signals of onlyfrequency f2 relating to the component carrier 2 (CoCa2); signals offrequency f1 are not boosted by the FSR. Consequently, when assumingthat the signal strength of the signal from the FSR is greater than theone of the eNodeB (not shown), the component carrier 2 will be receivedby the user equipment via the frequency-selective repeater, whereas theUE receives the component carrier 1 (CoCa1) directly from the eNodeB.This leads to different propagation delays between the two componentcarriers.

Therefore, there is a need of introducing more than one timing advancewithin one user equipment, i.e. separate timing advance may be requiredfor certain component carriers (Serving Cells).

One obvious solution is to perform a RACH procedure also on each of theSCells to achieve uplink synchronization, in a similar way to the PCell.Performing a RACH procedure on a SCell however would result in variousdisadvantages.

The power control/power allocation procedure is complicated whenconsidering simultaneous transmission of the PRACH and the PUSCH/PUCCHin one subframe, i.e. TTI. This might be the case where the uplink ofthe user equipment is out of synchronization on one component carrier,e.g. SCell, while still being uplink synchronized on another uplinkcomponent carrier, e.g. PCell. In order to regain uplink synchronizationfor the SCell, the user equipment performs a RACH access, e.g. orderedby PDCCH. Consequently, the user equipment transmits a RACH preamble,i.e. performs a PRACH transmission, and in the same TTI the userequipment also transmits PUSCH and/or PUCCH.

Currently, the power control loops for PUSCH/PUCCH and PRACH are totallyindependent, i.e. PRACH power is not considered when determiningPUSCH/PUCCH power, and vice versa. In order to deal with simultaneousPRACH and PUSCH/PUCCH transmissions, changes to the uplink power controlalgorithm are required. For instance, it would be necessary to considerthe PRACH transmission when power scaling needs to be used due to powerlimitation, since up to now only PUCCH, PUSCH with multiplexed uplinkcontrol information (UCI) and PUSCH without UCI are considered for thepower limitation case. PUCCH is given the highest priority over PUSCH,and the PUSCH with multiplexed UCI is considered to have a higherpriority over PUSCH without UCI.PUCCH>PUSCH w UCI>PUSCH w/o UCI

The prioritization rules for the power limitation case which are listedin the chapter relating to the Uplink Power Control would have to beextended by PRACH transmissions. However, there is no easystraightforward solution in said respect, since on the one hand uplinkcontrol information transmitted on PUCCH or PUSCH have a high priorityin order to allow for proper system operation, whereas on the other handPRACH should be also prioritized in order to ensure a high detectionprobability at the eNB in order to minimize the delay incurred by theRACH procedure.

In addition to the power control aspects, there is also a furtherdisadvantage regarding the power amplifier that would have to deal withthe simultaneous PRACH and PUSCH/PUCCH transmissions. There are certaindifferences in the uplink timing between the PRACH and the PUSCH/PUCCH,e.g. the timing advance for PRACH is of course 0; Guard Time, GT, whichis in the range of 96.88 μs to 715.63 μs. This is depicted in FIG. 22showing PUSCH transmissions on component carrier 0, and a correspondingPRACH transmission on component carrier 1.

Due to the Guard Time, there are power fluctuations within one subframe,which are undesirable. These power transients will add extra complexityto the implementation of the user equipment; in other words, the maximumpower reduction needs to also change during one subframe in order tofulfill the EMC requirements.

SUMMARY OF THE INVENTION

The present invention strives to avoid the various disadvantagesmentioned above.

One object of the invention is to propose a mechanism for aligning thetiming of uplink transmissions on uplink component carriers, wheredifferent propagation delays are imposed on the transmissions on theuplink component carriers. Another object of the invention is to suggesta mechanism for allowing a mobile terminal to perform time alignment ofuplink component carriers, without performing a random access procedure.

The object is solved by the subject matter of the independent claims.Advantageous embodiments are subject to the dependent claims. A furtherobject is to propose handover mechanisms that allow reducing thehandover delay due to time alignment of multiple uplink componentcarriers.

According to a first aspect of the invention, the mobile terminal timealigns a non-time aligned uplink cell (termed in the following targetcell) relative to a reference uplink cell which is already time-alignedand controlled by a same or a different aggregation access point as thetarget cell and transmits timing information, on which the procedure oftime aligning of the non-time aligned uplink target cell is based, tothe aggregation access point. It is assumed that at least one existingcell is already time-aligned and serves as reference cell for thetime-aligning procedure of the invention. Advantageously, the timinginformation transmitted to the aggregation access point can be used bythe aggregation access point for controlling the time-aligning processin the uplink target cell.

In more detail, instead of performing a random access channel, RACH,procedure, the mobile terminal time aligns uplink transmissions on thenon-time aligned uplink target cell by measuring particular timingdifference information. The particular timing difference informationenables the mobile terminal to extrapolate a time alignment for timealigning uplink transmissions of the mobile terminal on the uplinktarget cell.

The mobile terminal then calculates information on the necessary uplinktiming alignment to be used by the mobile terminal for time-aligning thetarget cell in relation to the reference cell which is alreadytime-aligned. For calculation of the timing advance, the mobile terminaluses at least the measurements and the timing advance of the referencecell.

Subsequently, the mobile terminal uses the calculated information toadjust the timing of its uplink transmissions on the uplink of thetarget cell relative to the timing advance value of the reference cell(value which is known by the mobile terminal).

The particular timing difference information can also be used by theaggregation access point to extrapolate a time alignment for uplinktransmissions of the mobile terminal on the uplink target cell. Inparticular, the timing advance of uplink transmission by the mobileterminal on the reference cell, which is used as a reference for timealigning the uplink target cell, is already known by the aggregationaccess point. Thus, the aggregation access point can also calculateinformation on the necessary uplink timing alignment to be used by themobile terminal for time-aligning the target cell in relation to thereference cell.

Reporting the particular timing difference information by the mobileterminal to the aggregation access point enables the aggregation accesspoint to track the time alignment to be used by the mobile terminal forthe uplink target cell. Likewise, reporting by the mobile terminal tothe aggregation access point the calculated information on the necessaryuplink timing alignment to be used for time-aligning the target cellalso achieves that the aggregation access point knows of the timealignment to be used by the mobile terminal for the uplink target cell.

The knowledge of the time alignment to be used by the mobile terminalfor the uplink target cell can advantageously be used by the aggregationaccess point for various effects as will become apparent from thedescription of the detailed embodiments.

One exemplary embodiment is related to a method for time aligning uplinktransmissions by a mobile terminal in a mobile communication system. Themobile terminal is in communication with an aggregation access point andbeing configured with a time-aligned uplink reference cell and with anon-time-aligned uplink target cell.

In this method, the mobile terminal measures transmission and/orreception time difference information relating to transmissions on thetarget cell and/or reference cell, determines a first target timingadvance based on at least the measured transmission and/or receptiontime difference information and on a reference timing advance used foruplink transmissions on the time-aligned reference cell, time-aligns theuplink target cell by adjusting a timing for uplink transmissions on theuplink target cell based on the determined first target timing advance,and transmits the measurement results and/or the first target timingadvance from the mobile terminal to the aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminal,repeats the steps of (i) measuring the transmission and/or receptiontime difference information, (ii) determining the first target timingadvance, (iii) time-aligning the uplink target cell, and (iv)transmitting the measurement results and/or the first target timingadvance based on a timer included in the mobile terminal, unlessotherwise instructed by the aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the aggregation accesspoint instructs the mobile terminal otherwise based on apre-configuration of the aggregation access point and/or on anevaluation step performed by the aggregation access point, bytransmitting to the mobile terminal at least one of: a random accesschannel, RACH, order message for the uplink target cell, for orderingthe mobile terminal to perform a random access procedure; a secondtarget timing advance, determined by the aggregation access point basedon at least the received measurement results and/or the received firsttarget timing advance and on a reference timing advance used for uplinktransmissions on the time-aligned reference cell; and a timing advanceupdate command for the uplink target cell, including a target timingadvance update value being determined based on at least the receivedmeasurement results and/or the received first target timing advance andon a timing of uplink transmissions on the uplink target cell beingtime-aligned based on the first target timing advance.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, in case the aggregationaccess point transmits a RACH order message, the mobile terminal, uponreception thereof, performs a random access procedure on the uplinktarget cell for determining a third target timing advance value foruplink transmission on the uplink target cell, and time-aligns theuplink target cell by adjusting a timing for uplink transmissions on theuplink target cell based on the determined third target timing advancereceived within the random access procedure.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, in case the aggregationaccess point determines a second target timing advance, and transmitsthe second target timing advance to the mobile terminal, the mobileterminal, upon reception thereof, performs the step of time-aligning theuplink target cell by adjusting a timing for uplink transmissions on theuplink target cell based on the second target timing advance receivedfrom the aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, in case the aggregationaccess point transmits a timing advance update command for the uplinktarget cell, the mobile terminal, upon reception thereof, determines afourth target timing advance based on the included target timing advanceupdate value and on the timing advance used for uplink transmissions onthe uplink target cell, and time-aligns the uplink target cell byadjusting a timing for uplink transmissions on the uplink target cellbased on the determined fourth target timing advance.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminalperforms the step of measuring the transmission and/or reception timedifference information and the step of determining the first targettiming advance in case the mobile terminal receives from the aggregationaccess point, information, preferably as a RRC message configuring thetarget cell, indicating that uplink transmissions on the uplink targetcell require a different time alignment than that used for the referencecell. Alternatively, the step of measuring the transmission and/orreception time difference information and the step of determining thefirst target timing advance are also performed, in case the mobileterminal receives from the aggregation access point, informationindicating a timing advance group for the target cell which is differentfrom the timing advance group of the reference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the aggregation accesspoint performs an evaluation step for determining a misalignment ofuplink transmissions on the uplink target cell by comparing a receptiontime of uplink transmissions on the uplink target cell with a predefinedreference time for uplink transmission on the uplink target cell, or bycomparing a reception time of uplink transmissions on the uplink targetcell with a transmission time of downlink transmissions on thecorresponding downlink target cell, or by comparing the receivedmeasurement result and/or first target timing advance to a predefinedthreshold value.

In case the determined misalignment is greater than a predefinedmisalignment threshold, the aggregation access point transmits to themobile terminal at least one of: the RACH order message, the secondtarget timing advance, and the timing advance update command.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the aggregation accesspoint is pre-configured to transmit, upon reception of the measurementresult and/or the first target timing advance and/or expiration of atimer, to the mobile terminal at least one of: the RACH order message,the second target timing advance, and the timing advance update command.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the reference cell isinitially time-aligned by performing a random access procedure betweenthe mobile terminal and the aggregation access point on the referencecell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminalmeasures by determining a downlink reception time difference(Δ_(Scell-PCell)Rx_(DL)) between the target and reference cell, bymeasuring the time between the beginning of a first downlink subframe onthe target cell (T_(DL) _(_) _(RX) _(_) _(SCell)) and the beginning ofthe corresponding downlink subframe on the reference cell (T_(DL) _(_)_(RX) _(_) _(PCell)), wherein downlink subframes on the reference andtarget cell refer to the same subframe number. The measurement resultsmay optionally be transmitted to the aggregation access point,comprising the downlink reception time difference between the target andreference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminalperforms the measurement by determining by the mobile terminal areception transmission time difference between the target and referencecell (Δ_(Scell-PCell)Rx_(DL)−Tx_(UL)) by measuring the time differencebetween the time when the mobile terminal transmits an uplink radioframe on the reference cell (T_(UL) _(_) _(TX) _(_) _(PCell)) and thetime when the mobile terminal receives a downlink radio frame on thetarget cell (T_(DL) _(_) _(RX) _(_) _(SCell)), wherein the uplink radioframe and the downlink radio frame relate to the same radio frame. Themeasurement results may optionally be transmitted to the aggregationaccess point, comprising the reception transmission time differencebetween the target and reference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminaldetermines the first target timing advance by determining a downlinkreception time difference between the target cell and the reference cell(Δ_(Scell-PCell)Rx_(DL)) subtracting the reception transmission timedifference from the timing advance of the reference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminaldetermines the first target timing advance based on the downlinkreception time difference.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the aggregation accesspoint determines a second target timing advance, based on a downlinktransmission time difference (Δ_(Scell-PCell)Tx_(DL)) between the targetcell and the reference cell. The downlink transmission time differenceis between the target cell and the reference cell is the time differencebetween the beginning of a downlink subframe on the reference cell(T_(DL) _(_) _(TX) _(_) _(PCell)) and the beginning of the correspondingdownlink subframe on the target cell (T_(DL) _(_) _(TX) _(_) _(SCell)),wherein the downlink subframes refer to the same subframe number.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminaltime-aligns the target cell by setting the transmission of uplink radioframes on the uplink target cell relative to the beginning of downlinkradio frames received via the downlink target cell, using the first,second, third or fourth target timing advance determined consideringthat the setting of the transmission of the uplink radio frames on theuplink target cell will be relative to the beginning of downlink radioframes received via the downlink target cell, respectively.

Or, the mobile terminal time-aligns the target cell by setting thetransmission of uplink radio frames on the uplink target cell relativeto the beginning of downlink radio frames received via the downlinkreference cell, using the first, second, third or fourth target timingadvance determined considering that the setting of the transmission ofthe uplink radio frames on the uplink target cell will be relative tothe beginning of downlink radio frames received via the downlinkreference cell.

Or, the mobile terminal time-aligns the target cell by setting thetransmission of uplink radio frames on the uplink target cell relativeto the beginning of uplink radio frames transmitted via the uplinkreference cell, using the first, second, third or fourth target timingadvance determined considering that the setting of the transmission ofthe uplink radio frames on the uplink target cell will be relative tothe beginning of uplink radio frames transmitted via the uplinkreference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminaltransmits the measurement results to the aggregation access point on thephysical uplink shared channel, PUSCH, of the reference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminaltransmits the measurement results as part of the radio resource controllayer, RRC, or of the medium access control layer, MAC, and in case itis part of the MAC layer, the measurement results are preferablytransmitted within a MAC control element.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the step of measuringthe time difference information by the mobile terminal and oftransmitting the measurement results to the aggregation access point is:

-   -   performed periodically, and/or    -   triggered by predetermined events, such as:        -   i. configuration and/or activation of the target cell        -   ii. the measurement results exceed a predetermined threshold        -   iii. expiry of a timing advance timer        -   iv. receiving a measurement reporting request from the            aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the measurementreporting request from the aggregation access point is:

-   -   a deactivation/activation command for deactivating/activating a        configured cell, including a flag indicating the request for        measurement reporting, the flag preferably being set in one of        the reserved bits of the deactivation/activation command, or    -   a radio resource control connection reconfiguration message,        including a flag indicating the request for measurement        reporting, or    -   a random access channel, RACH, order message, or    -   a random access channel, RACH, order message, with a        predetermined codepoint or a predetermined combination of        codepoints indicating the request for measurement reporting.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, in case the aggregationaccess point determines a second target timing advance, the aggregationaccess point transmits the second target timing advance within a mediumaccess control, MAC, control element, and preferably the second targettiming advance is transmitted using the downlink shared channel.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, in case the aggregationaccess point determines a second target timing advance, the secondtarget timing advance is an absolute value not to be used in relation tothe reference timing advance value of the reference cell, by the step oftime-aligning the uplink target cell being only based on the absolutevalue of the second target timing advance. Or the second target timingadvance is a relative value to be used relative to the reference timingadvance value of the reference cell, by the step of time-aligning theuplink target cell being also based on the reference timing advance.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the reference cell is aprimary cell or one of a plurality of secondary cells, and the targetcell is one of a plurality of secondary cells.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminalperforms the step of time-aligning for each target cell of a timingadvance group where the target cell is one out of a plurality of targetcells forming a group, and based on the same second target timingadvance received from the aggregation access point, based on the samefirst target timing advance determined by the mobile terminal or basedon the same fourth target timing advance determined by the mobileterminal in case of reception of timing advance update command foruplink transmissions on the uplink target cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminal isconfigured with a plurality of non-time-aligned target cells, and themobile terminal performs the time-alignment according to one of thevarious exemplary embodiments described herein for each of the targetcells.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the mobile terminaltransmits measurement results for each of the target cells to theaggregation access point within one message, preferably for allsecondary cells that are configured or all secondary cells that areconfigured and activated.

The present invention further provides a mobile terminal fortiming-aligning uplink transmissions in a mobile communication system.The mobile terminal is in communication with an aggregation access pointand is configured with a time-aligned uplink reference cell and with anon-time-aligned uplink target cell. A processor of the mobile terminalmeasures transmission and/or reception time difference informationrelating to transmissions on the target cell and/or reference cell. Theprocessor determines a first target timing advance based on at least themeasured transmission and/or reception time difference information andon a reference timing advance used for uplink transmissions on thetime-aligned reference cell. The processor an a transmitter of themobile terminal time-align the uplink target cell by adjusting a timingfor uplink transmissions on the uplink target cell based on thedetermined first target timing advance. The transmitter transmits themeasurement results and/or the first target timing advance from themobile terminal to the aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, wherein based on thetimer, the processor and transmitter of the mobile terminal repeatmeasuring the transmission and/or reception time difference information,determining the first target timing advance, time-aligning the uplinktarget cell, and transmitting the measurement results and/or the firsttarget timing advance, unless the receiver of the mobile terminalreceives an instruction from the aggregation access point instructingthe mobile terminal otherwise.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, a receiver of the mobileterminal receives from the aggregation access point a RACH ordermessage. The processor, transmitter and receiver perform, upon receptionof the RACH order message, a random access procedure on the uplinktarget cell for determining a third target timing advance value foruplink transmission on the uplink target cell. The processor andtransmitter time-align the uplink target cell by adjusting a timing foruplink transmissions on the uplink target cell based on the determinedthird target timing advance received within the random access procedure.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, a receiver of the mobileterminal receives from the aggregation access point a second targettiming advance. The processor and transmitter time-align, upon receptionof the second target timing advance, the uplink target cell by adjustinga timing for uplink transmissions on the uplink target cell based on thesecond target timing advance received from the aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, a receiver of the mobileterminal receives a timing advance update command for the uplink targetcell. The processor, upon reception of the timing advance updatecommand, determines a fourth target timing advance based on the includedtarget timing advance update value and on the timing advance used foruplink transmissions on the uplink target cell. Then, the processor andtransmitter time-align the uplink target cell by adjusting a timing foruplink transmissions on the uplink target cell based on the determinedfourth target timing advance.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor andtransmitter measure the transmission and/or reception time differenceinformation and the processor is adapted to determining the first targettiming advance in case a receiver of the mobile terminal receives, fromthe aggregation access point, information, preferably as a RRC messageconfiguring the target cell, indicating that uplink transmissions on theuplink target cell require a different time alignment than that used forthe reference cell, or receives, from the aggregation access point,information indicating a timing advance group for the target cell whichis different from the timing advance group of the reference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, wherein the referencecell is initially time-aligned by the processor, transmitter andreceiver performing a random access procedure between the mobileterminal and the aggregation access point on the reference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor determinesa downlink reception time difference (Δ_(Scell-PCell)Rx_(DL)) betweenthe target and reference cell, by measuring the time between thebeginning of a first downlink subframe on the target cell (TDL_RX_SCell)and the beginning of the corresponding downlink subframe on thereference cell (TDL_RX_PCell), wherein downlink subframes on thereference and target cell refer to the same subframe number, andoptionally the transmitter is adapted to transmit downlink receptiontime difference between the target and reference cell as the measurementresults to the aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor determinesa reception transmission time difference between the target andreference cell (Δ_(Scell-PCell)Rx_(DL)−Tx_(UL)), by measuring the timedifference between the time when the mobile terminal transmits an uplinkradio frame on the reference cell (TUL_TX_PCell) and the time when themobile terminal receives a downlink radio frame on the target cell(TDL_RX_SCell), wherein the uplink radio frame and the downlink radioframe relate to the same radio frame, and optionally the transmitter isadapted to transmit the reception transmission time difference betweenthe target and reference cell as the measurement results to theaggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor determinesa downlink reception time difference between the target cell and thereference cell (Δ_(Scell-PCell)Rx_(DL)) by subtracting the receptiontransmission time difference from the timing advance of the referencecell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor determinesthe first target timing advance based on the downlink reception timedifference.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor andtransmitter time-align the target cell setting the transmission ofuplink radio frames on the uplink target cell relative to the beginningof downlink radio frames received via the downlink target cell, usingthe first, second, third or fourth target timing advance determinedconsidering that the setting of the transmission of the uplink radioframes on the uplink target cell will be relative to the beginning ofdownlink radio frames received via the downlink target cell,respectively.

Or the processor and transmitter time-align the target cell setting thetransmission of uplink radio frames on the uplink target cell relativeto the beginning of downlink radio frames received via the downlinkreference cell, using the first, second, third or fourth target timingadvance determined considering that the setting of the transmission ofthe uplink radio frames on the uplink target cell will be relative tothe beginning of downlink radio frames received via the downlinkreference cell.

Or the processor and transmitter time-align the target cell setting thetransmission of uplink radio frames on the uplink target cell relativeto the beginning of uplink radio frames transmitted via the uplinkreference cell, using the first, second, third or fourth target timingadvance determined considering that the setting of the transmission ofthe uplink radio frames on the uplink target cell will be relative tothe beginning of uplink radio frames transmitted via the uplinkreference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the transmittertransmits the measurement results to the aggregation access point on thephysical uplink shared channel, PUSCH, of the reference cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the transmittertransmits measurement results as part of the radio resource controllayer, RRC, or of the medium access control layer, MAC, and in case itis part of the MAC layer, the measurement results are preferablytransmitted within a MAC control element.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor and thetransmitter measure the time difference information, to determine afirst target timing advance and transmit the measurement results and/orthe first target timing advance to the aggregation access point:

-   -   periodically, and/or    -   by predetermined events, such as:        -   i. configuration and/or activation of the target cell        -   ii. the measurement results exceed a predetermined threshold        -   iii. expiry of a timing advance timer        -   iv. receiving a measurement reporting request from the            aggregation access point.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the receiver receives

-   -   a deactivation/activation command as the measurement reporting        request from the aggregation access point for        deactivating/activating a configured cell, including a flag        indicating the request for measurement reporting, the flag        preferably being set in one of the reserved bits of the        deactivation/activation command, or    -   a radio resource control connection reconfiguration message as        the measurement reporting request from the aggregation access        point, including a flag indicating the request for measurement        reporting, or    -   a random access channel, RACH, order message as the measurement        reporting request from the aggregation access point, or    -   a random access channel, RACH, order message as the measurement        reporting request from the aggregation access point, with a        predetermined codepoint or a predetermined combination of        codepoints indicating the request for measurement reporting.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the reference cell is aprimary cell or one of a plurality of secondary cells, and the targetcell is one of a plurality of secondary cells.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor andtransmitter time-align each target cell of a timing advance group basedon the same second target timing advance received from the aggregationaccess point, based on the same first target timing advance determinedby the mobile terminal or based on the same fourth target timing advancedetermined by the mobile terminal in case of reception of timing advanceupdate command for uplink transmissions on the uplink target cell.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, in case the mobileterminal is configured with a plurality of non-time-aligned targetcells, the mobile terminal performs the time-alignment according to oneof the various exemplary embodiments described herein for each of thetarget cells.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the transmittertransmits the measurement results for each of the target cells istransmitted to the aggregation access point within one message,preferably for all secondary cells that are configured or all secondarycells that are configured and activated.

The present invention further provides an aggregation access point forcontrolling time aligning a mobile terminal in a mobile communicationsystem, the mobile terminal being in communication with the aggregationaccess point and being configured with a time-aligned uplink referencecell and with a non-time-aligned uplink target cell. A memory of theaggregation access point stores a pre-configuration. A receiver of theaggregation access point receives measurement results and/or a firsttarget timing advance. A processor of the aggregation access pointdetermines based on at least the received measurement results and/or thereceived first target timing advance and on a reference timing advanceused for uplink transmissions on the time-aligned reference cell, and/oradapted to determine based on at least the received measurement resultsand/or the received first target timing advance and on a timing ofuplink transmissions on the uplink target cell being time-aligned basedon the first target timing advance. A transmitter may transmit aninstruction to the mobile terminal to instruct the mobile terminalotherwise, based on the pre-configuration of the aggregation accesspoint and/or on the processor performing an evaluation step bytransmitting at least one of:

-   -   a random access channel, RACH, order message for the uplink        target cell, for ordering the mobile terminal to perform a        random access procedure;    -   a second target timing advance, determined by the processor        based on at least the received measurement results and/or the        received first target timing advance and on a reference timing        advance used for uplink transmissions on the time-aligned        reference cell; and    -   a timing advance update command for the uplink target cell,        including a target timing advance update value being determined        based on at least the received measurement results and/or the        received first target timing advance and on a timing of uplink        transmissions on the uplink target cell being time-aligned based        on the first target timing advance.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor performsan evaluation step for determining a misalignment of uplinktransmissions on the uplink target cell, by comparing a reception timeof uplink transmissions on the uplink target cell with a predefinedreference time for uplink transmission on the uplink target cell, or bycomparing a reception time of uplink transmissions on the uplink targetcell with a transmission time of downlink transmissions on thecorresponding downlink target cell, or by comparing the receivedmeasurement result and/or first target timing advance to a predefinedthreshold value.

In case the determined misalignment is greater than a predefinedmisalignment threshold, the transmitter transmits to the mobile terminalat least one of: the RACH order message, the second target timingadvance, and the timing advance update command.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the aggregation accesspoint is pre-configured base on the memory so that the transmittertransmits, upon reception of the measurement result and/or the firsttarget timing advance and/or expiration of a timer, to the mobileterminal at least one of: the RACH order message, the second targettiming advance, and the timing advance update command.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor is adaptedto the second target timing advance further based on a downlinktransmission time difference (Δ_(Scell-PCell)Tx_(DL)) between the targetcell and the reference cell, wherein the downlink transmission timedifference between the target cell and the reference cell is the timedifference between the beginning of a downlink subframe on the referencecell (T_(DL) _(_) _(TX) _(_) _(PCell)) and the beginning of thecorresponding downlink subframe on the target cell (T_(DL) _(_) _(TX)_(_) _(SCell)), wherein the downlink subframes refer to the samesubframe number.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the transmittertransmits the second target timing advance within a medium accesscontrol, MAC, control element, and preferably, the downlink sharedchannel wherein the step of transmitting the second target timingadvance uses.

According to an advantageous embodiment of the invention which can beused in addition or alternatively to the above, the processor determinesa second target timing advance, the second target timing advance beingan absolute value not to be used in relation to the reference timingadvance value of the reference cell, or wherein the second target timingadvance is a relative value to be used relative to the reference timingadvance value of the reference cell.

The present invention further provides a computer readable mediumstoring instructions that, when executed by a processor of a mobileterminal, cause the mobile terminal to time align uplink transmissionsin a mobile communication system as follows. Transmission and/orreception time difference information relating to transmissions on thetarget cell and/or reference cell are measured. A first target timingadvance based on at least the measured transmission and/or receptiontime difference information and on a reference timing advance used foruplink transmissions on the time-aligned reference cell is determined.The uplink target cell is time-aligned by adjusting a timing for uplinktransmissions on the uplink target cell based on the determined firsttarget timing advance. The measurement results and/or the first targettiming advance from the mobile terminal are transmitted to theaggregation access point.

The computer readable medium stores instructions that, when executed bya processor of a mobile terminal, cause the mobile terminal to performthe steps of the above-described methods.

According to another aspect of the invention, the mobile terminal timealigns a non-time aligned uplink component carrier of a radio cellrelative to a reference cell in which a (reference) uplink componentcarrier is already time aligned. The determination of the timing advancefor time alignment of the non-time aligned uplink component carrier ofthe radio cell is thereby determined based on the timing advance for the(uplink component carrier of the) reference cell and the time differenceof the reception times (also referred to as “reception time difference”in the following) for corresponding downlink transmissions via thedownlink component carriers of the reference cell and the radio cellcomprising the non-time aligned uplink component carrier.

As will become apparent, the time alignment of the non-aligned uplinkcomponent carrier can be performed relative to the reception timing ofthe downlink component carrier of the reference cell or relative to thereception timing of the downlink component carrier of the radio cellcomprising the uplink component carrier.

One exemplary embodiment of the invention is related to a method fortime aligning uplink transmissions by a mobile terminal in a mobilecommunication system. The mobile terminal is configured with a firstradio cell comprising a downlink component carrier and a time aligneduplink component carrier, and a second radio cell comprising a downlinkcomponent carrier and a non-time aligned uplink component carrier.

In this method, the mobile terminal determines a reception timedifference (or propagation delay difference) for downlink transmissionsfrom an aggregation access point to the mobile terminal via the downlinkcomponent carrier of the first radio cell and via the downlink componentcarrier of the second radio cell, respectively, and time aligns theuplink component carrier of the second radio cell by adjusting a timingadvance for uplink transmissions on the uplink component carrier of thesecond radio cell based on the timing advance for uplink transmissionson the time aligned uplink component carrier of the first radio cell andthe determined reception time difference (or propagation delaydifference), so that uplink transmissions transmitted from the mobileterminal to the aggregation access point via the uplink componentcarrier of the first radio cell and the uplink component carrier of thesecond radio cell arrives at the aggregation access pointsimultaneously.

In one exemplary implementation of this embodiment, the downlinkcomponent carrier and the uplink component carrier of one of the radiocells may be for example established between the aggregation accesspoint and the mobile terminal, while the downlink component carrier andthe uplink component carrier of the other radio cell may be establishedbetween another access point and the mobile terminal.

The other access point could for example maintain a bi-directionalinterface to the aggregation access point via which transmissions fromand to the mobile terminal are forwarded to the aggregation accesspoint, respectively, to the mobile terminal.

In this exemplary implementation, the determined reception timedifference (or propagation delay difference) determined by the mobileterminal may for example account for a propagation delay oftransmissions between the aggregation access point and the other accesspoint, a processing delay of the other access point for processing thetransmissions to be forwarded and a propagation delay of transmissionsbetween the other access point and the mobile terminal.

In one exemplary implementation, the aggregation access point may be aneNodeB. In another implementation, the other access point could be forexample a Frequency Selective Repeater (FSR) or a Remote Radio Head(RRH) controlled by the aggregation access point.

According to a further embodiment of the invention, the uplink data istransmitted by the mobile terminal via the time aligned first componentcarrier and the time aligned second component carrier to the aggregationaccess point, which combines the uplink transmissions of the mobileterminal received via the time aligned first component carrier and thetime aligned second component carrier.

The combination of the uplink transmissions by the aggregation accesspoint may occur in one of different layers. For example, the combinationof the uplink data of the mobile terminal could be performed by the RLCentity of the aggregation access point. This may be for example the casein a scenario where the aggregation access point is an eNodeB and theother access point is a RRH.

Alternatively, the combination of the uplink data of the mobile terminalis performed by the physical layer entity of the aggregation accesspoint. This may be for example the case in a scenario where theaggregation access point is an eNodeB and the other access point is aFSR.

There a different possibilities how the uplink component carrier of thefirst radio cell becomes time aligned. In one exemplary embodiment ofthe invention, the uplink component carrier of the first radio cell istime aligned by the mobile terminal and an access point by performing arandom access procedure (also denoted: RACH procedure) configuring thetiming advance for the uplink component carrier of the first radio cell.Advantageously, the uplink component carrier of the second radio cell istime aligned without performing a random access procedure with an accesspoint. In one exemplary embodiment, the access point performing the RACHprocedure with the mobile terminal is the aggregation access point.

In one exemplary implementation the mobile terminal receives a commandfrom the aggregation access point to time align the uplink componentcarrier of the second radio cell based on the reception time difference(or propagation delay difference). For example, the command may beincluded within a RRC Radioresource Configuration Message.

The command may be for example signaled by means of a flag indicatingwhether the mobile terminal is to use a random access procedure for timealigning the uplink component carrier of the second radio cell orwhether to time align the uplink component carrier of the second radiocell based on the reception time difference (or propagation delaydifference) relative to a downlink component carrier of a referenceradio cell (i.e. using the terminology above, the downlink componentcarrier of the first cell).

In a further embodiment of the invention, the mobile terminal determinesa reception time difference (or propagation delay difference) for adownlink transmissions comprises calculating the reception timedifference (or propagation delay difference) by subtracting the time ofthe beginning of a sub-frame received via the downlink component carrierof the second cell from a time of the beginning of the next sub-framereceived via the downlink component carrier of the first cell. Thebeginning of the next sub-frame means the beginning of the nextsub-frame that is received via the downlink component carrier of thefirst cell after the point in time of the beginning of the sub-framereceived via the downlink component carrier of the second cell.

In another embodiment of the invention, for time alignment of the uplinkcomponent carriers of a mobile node, the mobile node could for examplemaintain a respective timing advance value for each uplink componentcarrier. In an alternative embodiment of the invention, a scenario isconsidered, where it is possible that plural component carriers have thesame propagation delay, then these component carriers can be grouped andbe associated with a respective timing advance value. Hence, in thiscase the mobile node may for example maintain a respective timingadvance value for each group of one or more uplink component carriers,wherein uplink transmissions on the one or more uplink componentcarriers of a group experience the same propagation delay.

In a further exemplary implementation, the timing advance values for theuplink component carriers are determined to ensure that an uplinktransmission via the uplink component carriers arrives at theaggregation access point simultaneously.

In one exemplary embodiment, the timing advance value for an uplinkcomponent carrier of a given radio cell may be considered to indicate atime shift for the transmission of uplink sub-frames on the uplinkcomponent carrier of the given radio cell relative to the beginning ofsub-frames received via the downlink component carrier of the givenradio cell (e.g. the second radio cell mentioned above). In analternative embodiment of the invention, the timing advance value for anuplink component carrier of a given radio cell may be considered toindicate a time shift for the transmission of uplink sub-frames on theuplink component carrier of the given radio cell relative to thebeginning of sub-frames received via the downlink component carrier ofthe reference cell (e.g. the first radio cell mentioned above).

In one exemplary embodiment of the invention, time aligning the uplinkcomponent carrier of the second radio cell comprises calculating atiming advance value for the uplink component carrier of the secondcell, TA_(AP2), based on the on the timing advance value for the timealigned uplink component carrier of the first radio cell, TA_(AP1), andthe determined reception time difference (or propagation delaydifference), ΔT_(prop), as follows:TA_(AP2)=TA_(AP1)+2·ΔT _(prop)

In this exemplary embodiment, the timing advance value TA_(AP2) isdefining the timing advance relative to the reception timing of thedownlink component carrier of the second radio cell (or to be moreprecise the relative to the reception timing of the beginning ofsub-frames transmitted via the downlink component carrier of the secondradio cell).

In another exemplary embodiment of the invention, time aligning theuplink component carrier of the second radio cell comprises calculatinga timing advance value for the uplink component carrier of the secondcell, TA_(AP2), based on the on the timing advance value for the timealigned uplink component carrier of the first radio cell, TA_(AP1), andthe determined reception time difference (or propagation delaydifference), ΔT_(prop), as follows:TA_(AP2)=TA_(AP1) +ΔT _(prop)

In this exemplary embodiment, the timing advance value TA_(AP2) isdefining the timing advance relative to the reception timing of thedownlink component carrier of the first radio cell (or to be moreprecise the relative to the reception timing of the beginning ofsub-frames transmitted via the downlink component carrier of the firstradio cell).

Another third aspect of the invention is to suggest a procedure for timealignment of uplink component carriers for use in a handover procedureof a mobile terminal. The time alignment procedure as discussed abovemay be also used for time aligning uplink component carriers in radiocells controlled by the target (aggregation) access point to which themobile terminal is handed over. According to this aspect, the timingadvance for one of the uplink component carriers in a radio cell (i.e.the reference cell) of the target (aggregation) access point may beeither provided to the mobile terminal (synchronized handover) or may bedetermined by the mobile terminal (non-synchronized handover), e.g. bymeans of performing a random access procedure. The other uplinkcomponent carrier(s) of the other radio cell(s) to be used by the mobileterminal may then be time aligned relative to the reference cell asdescribed previously herein.

In line with this third aspect and in accordance with a furtherembodiment of the invention, a method for performing a handover of amobile terminal to a target aggregation access point (e.g. a eNodeB) isprovided. The mobile terminal is to be configured, under control of thetarget aggregation access point, with a first radio cell comprising adownlink component carrier and an uplink component carrier, and a secondradio cell comprising a downlink component carrier and an uplinkcomponent carrier.

The mobile terminal performs a random access procedure with the targetaggregation access point to thereby time align the uplink componentcarrier of the first radio cell. The mobile terminal can then determinea reception time difference (or propagation delay difference) fordownlink transmissions from the target aggregation access point to themobile terminal via the downlink component carrier of the first radiocell and via the downlink component carrier of the second radio cell,and may time align the uplink component carrier of the second radio cellby adjusting a timing advance for uplink transmissions on the uplinkcomponent carrier of the second radio cell based on the timing advancefor uplink transmissions on the time aligned uplink component carrier ofthe first radio cell and the determined reception time difference (orpropagation delay difference), so that an uplink transmissiontransmitted from the mobile terminal to the aggregation access point viathe uplink component carrier of the first radio cell and via the uplinkcomponent carrier of the second radio cell arrives at the aggregationaccess point simultaneously.

Also in line with this third aspect and in accordance with anotherembodiment of the invention, a method for performing a handover of amobile terminal from a source access point to a target aggregationaccess point is provided. The mobile terminal is again assumed to beconfigured, under control of the target aggregation access point, with afirst radio cell comprising a downlink component carrier and an uplinkcomponent carrier, and a second radio cell comprising a downlinkcomponent carrier and an uplink component carrier.

In this method, the mobile terminal receives through a radio cellcontrolled by the source access point, a timing advance value thatindicated the time alignment to be applied by the mobile terminal touplink transmissions on the uplink component carrier of the first radiocell. The mobile terminal may further determine a reception timedifference (or propagation delay difference) for downlink transmissionsfrom the target aggregation access point to the mobile terminal via thedownlink component carrier of the first radio cell and via the downlinkcomponent carrier of the second radio cell, and may then time align theuplink component carrier of the second radio cell by adjusting a timingadvance for uplink transmissions on the uplink component carrier of thesecond radio cell based on the timing advance for uplink transmissionson the time aligned uplink component carrier of the first radio cell andthe determined reception time difference (or propagation delaydifference), so that an uplink transmission transmitted from the mobileterminal to the aggregation access point via the uplink componentcarrier of the first radio cell and via the uplink component carrier ofthe second radio cell arrives at the aggregation access pointsimultaneously.

The source access point and the target aggregation access point may befor example eNodeBs.

In another embodiment, the two handover methods above may furthercomprise the steps of the method for time aligning uplink transmissionsby a mobile terminal in a mobile communication system according to oneof the various exemplary embodiments described herein.

Another embodiment of the invention relates to a mobile terminal fortime aligning uplink transmissions in a mobile communication system. Themobile terminal is configured with a first radio cell comprising adownlink component carrier and a time aligned uplink component carrier,and a second radio cell comprising a downlink component carrier and anon-time aligned uplink component carrier. In this embodiment, themobile terminal comprises a receiver unit adapted to receive downlinktransmissions, and a processing unit adapted to determine a receptiontime difference (or propagation delay difference) for a downlinktransmission from an aggregation access point to the mobile terminal viathe downlink component carrier of the first radio cell and via thedownlink component carrier of the second radio cell, respectively. Theprocessing unit time aligns the uplink component carrier of the secondradio cell by adjusting a timing advance for uplink transmissions on theuplink component carrier of the second radio cell based on the timingadvance for uplink transmissions on the time aligned uplink componentcarrier of the first radio cell and the determined reception timedifference (or propagation delay difference). Further, the mobileterminal comprises a transmitter unit adapted to transmit an uplinktransmission to the aggregation access point via the time aligned uplinkcomponent carrier of the first radio cell and the time aligned uplinkcomponent carrier of the second radio cell so that uplink transmissionvia the time aligned uplink component carrier of the first radio celland the time aligned uplink component carrier of the second radio cellarrives at the aggregation access point simultaneously.

The mobile terminal according to a more detailed embodiment of theinvention is adapted to perform a handover to the aggregation point. Thereceiver unit of the mobile terminal is adapted to receive, through aradio cell controlled by a source access point, a timing advance valuethat indicated the time alignment to be applied by the mobile terminalto uplink transmissions on the uplink component carrier of the firstradio cell.

In alternative implementation, the mobile terminal is adapted to performa handover from a source access point to the aggregation point, and toperform a random access procedure with the aggregation access point tothereby time align the uplink component carrier of the first radio cell.

Another embodiment of the invention is providing a computer readablemedium storing instructions that, when executed by a processor of amobile terminal, cause the mobile terminal to time align uplinktransmissions in a mobile communication system, by determining by themobile terminal a reception time difference (or propagation delaydifference) for downlink transmissions from an aggregation access pointto the mobile terminal via a downlink component carrier of a first radiocell and via a downlink component carrier of a second radio cell,respectively, wherein the mobile terminal is configured with the firstradio cell comprising the downlink component carrier and a time aligneduplink component carrier, and the second radio cell comprising thedownlink component carrier and a non-time aligned uplink componentcarrier, and time aligning the uplink component carrier of the secondradio cell by adjusting a timing advance for uplink transmissions on theuplink component carrier of the second radio cell based on the timingadvance for uplink transmissions on the time aligned uplink componentcarrier of the first radio cell and the determined reception timedifference (or propagation delay difference), so that uplinktransmissions transmitted from the mobile terminal to the aggregationaccess point via the uplink component carrier of the first radio celland the uplink component carrier of the second radio cell arrives at theaggregation access point simultaneously.

The computer readable medium according to further embodiment of theinvention is storing instructions that, when executed by a processor ofa mobile terminal, cause the mobile terminal to perform the steps of themethod for time aligning uplink transmissions by a mobile terminal in amobile communication system according to one of the various exemplaryembodiments described herein.

BRIEF DESCRIPTION OF THE FIGURES

In the following the invention is described in more detail in referenceto the attached figures and drawings. Similar or corresponding detailsin the figures are marked with the same reference numerals.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system,

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE,

FIG. 3 shows an exemplary sub-frame boundaries on a downlink componentcarrier as defined for 3GPP LTE (Release 8/9),

FIG. 4 shows an exemplary downlink resource grid of a downlink slot asdefined for 3GPP LTE (Release 8/9),

FIGS. 5 & 6 show the 3GPP LTE-A (Release 10) Layer 2 structure withactivated carrier aggregation for the downlink and uplink, respectively,

FIG. 7 shows a RACH procedures as defined for 3GPP LTE (Release 8/9) inwhich contentions may occur, and

FIG. 8 shows a contention-free RACH procedure as defined for 3GPP LTE(Release 8/9),

FIG. 9 exemplifies the time alignment of an uplink component carrierrelative to a downlink component carrier by means of a timing advance asdefined for 3GPP LTE (Release 8/9),

FIGS. 10 & 11 exemplify the interruption time during a non-synchronizedand synchronized handover, respectively, due to time alignment ofmultiple uplink component carriers,

FIG. 12 exemplifies the reduction of the interruption time caused by asynchronous handover, when employing the time alignment calculation ofuplink component carriers according to one of the various embodimentsdescribed herein,

FIG. 13 shows an exemplary scenario in which a user equipmentsaggregates two radio cells, one radio cell originating from an eNodeB,and the other radio cell originating from a Remote Radio Head (RRH),

FIG. 14 shows an exemplary scenario in which a user equipmentsaggregates two radio cells, one radio cell originating from an eNodeB,and the other radio cell originating from a Frequency Selective Repeater(FSR),

FIGS. 15 to 17 show a exemplary procedures according to differentexemplary embodiments of the invention allowing the user equipment todetermine the correct time alignment for non-time aligned uplinkcomponent carriers in other radio cells than the reference cell,

FIG. 18 shows an exemplifies the structure of a sub-frame according toone exemplary embodiment of the invention, and the transmissions thereofvia three component carriers,

FIG. 19 exemplifies the time alignment of three uplink transmissions fora single sub-frame using different timing advance values, so as to timealign their reception at an aggregation access point,

FIG. 20 shows the format of an activation/deactivation MAC controlelement, being a command for activating or deactivating one or moreSCells,

FIG. 21 shows the format of an Extended Power Headroom MAC controlelement, when Type 2 PHR is reported,

FIG. 22 illustrates the disadvantage of using a PRACH transmission on acomponent carrier to be uplink-time-aligned, and in particular, thedifferences in the uplink timing between PRACH on one component carrierand PUSCH/PUCCH on the another component carrier,

FIG. 23 is a signaling diagram illustrating an uplink-time-alignmentprocedure according to one embodiment of the invention,

FIG. 24 presents the network scenario assumed for one particularembodiment of the invention,

FIG. 25 shows a signaling diagram illustrating an uplink-time-alignmentprocedure according to another embodiment of the invention,

FIG. 26 shows a timing diagram of transmissions exchanged between the UEand the eNodeB, including uplink-time-aligned uplink transmissionaccording to one embodiment of the invention,

FIG. 27 shows a timing diagram of transmissions exchanged between the UEand the eNodeB, including uplink-time-aligned uplink transmissionsaccording to another embodiment of the invention, wherein the PCell andSCell downlink transmission are time-delayed,

FIG. 28 is a flowchart diagram illustrating an uplink-time-alignmentprocedure according to a further embodiment of the invention,

FIG. 29 shows a format of a MAC control element for transmitting themeasurement results from the mobile terminal to the eNodeB, themeasurement results being the downlink reception time differencesbetween the PCell and all the SCells,

FIG. 30 shows a format of a MAC control element for transmitting themeasurement results from the mobile terminal to the eNodeB, themeasurement results being the reception transmission time differencesbetween the PCell and all the SCells,

FIG. 31 illustrates the uplink time alignment process performed at themobile terminal, in case the timing advance command received from theeNodeB is calculated relative to the beginning of an uplink radio frameof the PCell, according to one embodiment of the invention,

FIG. 32 illustrates the uplink time alignment process performed at themobile terminal, in case the timing advance command received from theeNodeB is calculated relative to the beginning of a downlink radio frameof the PCell, according to one embodiment of the invention, and

FIG. 33 shows the format of a timing advance command according to oneembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following paragraphs will describe various embodiments of theinvention. For exemplary purposes only, most of the embodiments areoutlined in relation to an orthogonal single-carrier uplink radio accessscheme according to 3GPP LTE (Release 8/9) and LTE-A (Release 10) mobilecommunication systems discussed in the Technical Background sectionabove. It should be noted that the invention may be advantageously usedfor example in a mobile communication system such as 3GPP LTE (Release8/9) and LTE-A (Release 10) communication systems as described in theTechnical Background section above, but the invention is not limited toits use in this particular exemplary communication network. Theinvention may be broadly used in communication systems where timealignment of uplink transmissions on multiple carriers (having differentpropagation delays) is desired.

The explanations given in the Technical Background section above areintended to better understand the mostly 3GPP LTE (Release 8/9) andLTE-A (Release 10) specific exemplary embodiments described herein andshould not be understood as limiting the invention to the describedspecific implementations of processes and functions in the mobilecommunication network.

One aspect of the invention is to time align a non-time aligned uplinkcomponent carrier of a radio cell relative to a reference cell in whicha (reference) uplink component carrier is already time aligned. Thetiming advance for time alignment of the non-time aligned uplinkcomponent carrier of the radio cell is determined based on the timingadvance for the uplink component carrier of the reference cell and thetime difference of the reception times (or propagation delay difference)for corresponding downlink transmissions via the downlink componentcarriers of the reference cell and the radio cell comprising thenon-time aligned uplink component carrier. The time alignment mechanismmay be used for time aligning transmissions on uplink component carriersthat are newly configured or activated by a mobile terminal or that mayrequire reestablishment of the time alignment (e.g. after loosing same).As will be outlined below, the new configuration of uplink componentcarriers may for example result from a handover of the mobile terminalto a target access point or an operation of configuring or activating anadditional uplink component carrier at the mobile terminal.

Corresponding downlink transmissions may for example denotetransmissions that are sent simultaneously by an access point via thedownlink component carrier of the reference cell and via the radio cellcomprising the non-time aligned uplink component carrier (e.g.transmissions of a given sub-frame sent via the two downlink componentcarriers). In this case the reception time difference is also the timedifference of the propagation delay of the transmission sent via thedownlink component carrier of the reference cell and propagation delayof the transmission sent via the downlink component carrier of the radiocell comprising the non-time aligned uplink component carrier (alsoreferred to as “propagation delay difference” in the following). Hence,in this case the determination of the timing advance for time alignmentof the non-time aligned uplink component carrier of the radio cell isdetermined based on the timing advance for the (uplink component carrierof the) reference cell and the propagation delay difference of downlinktransmissions via the downlink component carriers of the reference celland the radio cell comprising the non-time aligned uplink componentcarrier.

For the purpose of time alignment, it is—strictly speaking—not necessarythat the reference cell is configured an uplink component carrier. Itwould be sufficient that the mobile terminal is provided with areference timing advance value to be used, and further there is downlinkcomponent carrier received through the reference cell, based on whichthe reception time difference (or propagation delay difference) can bedetermined for time aligning the other radio cells. However, for mostpractical implementations it may be advantageous is the reference cellis configured with a downlink component carrier and a (time aligned)uplink component carrier.

Furthermore, in one embodiment of the invention, the reference cellrelative to which the timing of the non-time aligned uplink componentcarrier(s) is a radio cell comprising a time-aligned uplink componentcarrier between the user equipment and the aggregation access point.However, the reference cell may also be a radio cell comprising atime-aligned uplink component carrier between the user equipment andanother access point than the aggregation access point. The termaggregation access point (for example a base station or eNodeB) is usedto denote location in the access network, i.e. a node, at which theuplink transmissions of the user equipment on the different uplinkcomponent carriers are aggregated. Aggregation refers to

-   -   a simultaneous reception of the radio signals corresponding to        transmissions (e.g. respective sub-frames) on the different        uplink component carriers from the user equipment, i.e. on the        physical layer, for joint physical layer processing (e.g. joint        demodulation (e.g. including utilization of one IFFT (Inverse        Fast Fourier Transform) for the processing of the received        sub-frame in an OFDM system) and/or joint decoding of coded        transport block(s), etc.) by the aggregation access point;        and/or    -   a processing of protocol data units received in the        transmissions (e.g. respective sub-frames) on the different        uplink component carriers from the user equipment in a protocol        entity of the aggregation access point.

The conjoint processing of protocol data units received in thetransmissions on the different uplink component carriers from the userequipment may be in one exemplary implementation the conjoint processingof PDUs obtained from the transmissions on the different uplinkcomponent carriers in the MAC layer or RLC layer of the aggregationaccess point, e.g. for the purpose of PDU reordering.

In other words, in one exemplary embodiment of the invention, theaggregation access point denotes the network node which is to receivethe radio signals corresponding to transmissions (e.g. respectivesub-frames) on the different uplink component carriers, i.e. on thephysical layer, from the user equipment for joint processing (e.g.demodulation and/or decoding) by the aggregation access point. Inanother exemplary embodiment of the invention, the aggregation accesspoint denotes the network node which should processes protocol dataunits received in the transmissions (e.g. respective sub-frames) via thedifferent uplink component carriers from the user equipment. In oneexemplary implementation, the aggregation access point is a base stationor eNodeB.

In line with this first aspect of the invention and according to anexemplary embodiment of the invention a method for time aligning uplinktransmissions by a mobile terminal in a mobile communication system isprovided. The mobile terminal is configured with a first radio cellcomprising a downlink component carrier and a time aligned uplinkcomponent carrier, and a second radio cell comprising a downlinkcomponent carrier and a non-time aligned uplink component carrier. Themobile terminal determines a reception time difference (or propagationdelay difference) for downlink transmissions from an aggregation accesspoint to the mobile terminal via the downlink component carrier of thefirst radio cell and via the downlink component carrier of the secondradio cell, respectively, and time aligns the uplink component carrierof the second radio cell by adjusting a timing advance for uplinktransmissions on the uplink component carrier of the second radio cellbased on the timing advance for uplink transmissions on the time aligneduplink component carrier of the first radio cell and the determinedreception time difference (or propagation delay difference), so thatuplink transmissions transmitted from the mobile terminal to theaggregation access point via the uplink component carrier of the firstradio cell and the uplink component carrier of the second radio cellarrives at the aggregation access point simultaneously. Hence, no RACHprocedure is needed for time alignment of the uplink component carrierin the second radio cell.

In this document, simultaneously or at the same point in time means atthe same point in time plus/minus some deviation, which is in the μsrange. For example, minor differences between uplink and downlinkpropagation delays in a given radio cell as well as the granularity oftiming advance values imply that there is no perfect time alignment ofthe uplink transmissions on uplink component carriers. In any casesimultaneous arrival of uplink transmissions is ensured to the extentthat the uplink transmissions by a mobile terminal via distinct uplinkcomponent carriers (having different propagation delays) can beprocessed together by the receiving aggregation access point. Forexample, different transmissions of one given sub-frame on the uplinkcomponent carriers are time aligned such that they are received in amanner allowing the aggregation access point to process alltransmissions of the sub-frame together (joint processing).

Furthermore, it should also be noted that time alignment of uplinkcomponent carriers that are configured for a mobile terminal is ofcourse also applicable, where the mobile terminal has to time align morethan one uplink component carrier. Basically, an arbitrary number ofuplink component carriers can be time aligned by the proceduresdescribed herein, as long as there is one reference time advance for anuplink component carrier.

Moreover, it should be noted that a single radio cell may comprise oneor more uplink component carrier and one or more downlink componentcarriers. In one radio cell it may be the case that the propagationdelay of all uplink and downlink component carriers can be assumedidentical. Accordingly, the uplink component carriers of a radio cellcan be considered to form a group of uplink component carriers thatexperience the same propagation delay and that may be associated to asingle timing advance value. Of course, if the propagation delays of theuplink component carriers differ from each other within a radio cell(e.g. due to using a FSR), then a timing advance value for eachexperienced propagation delay should be provided.

Another second aspect of the invention is to suggest a procedure fortime alignment of uplink component carriers for use in a handoverprocedure of a mobile terminal. Procedures are provided for synchronousand non-synchronous handover. The time alignment procedure as discussedabove may be also used for time aligning uplink component carriers inradio cells controlled by the target (aggregation) access point to whichthe mobile terminal is handed over. According to this aspect, the timingadvance for one of the uplink component carriers in a radio cell (i.e.the reference cell) of the target (aggregation) access point may beeither provided to the mobile terminal (synchronized handover) or may bedetermined by the mobile terminal (non-synchronized handover), e.g. bymeans of performing a random access procedure. The other uplinkcomponent carrier(s) of the other radio cell(s) to be used by the mobileterminal may then be time aligned relative to the reference cell asdescribed previously herein.

In case a mobile terminal, also denoted user equipment in the 3GPPterminology, is aggregating component carriers that stem from sources indifferent bands and physical locations, due to different propagationconditions these component carriers all might have differentpropagations delay.

Under the premises that an aggregation access point (e.g. eNodeB) isprocessing the uplink transmissions via all configured componentcarriers of a given mobile terminal, the uplink transmissions from themobile terminal should arrive simultaneously (at the point in time) atthe aggregation access point even though the propagation delays on thecomponent carriers are different. Hence the aggregation access pointcould configure the mobile terminal with a different timing advance foreach uplink component carrier depending on it's specific propagationdelay. The propagation delay is likely to be the same for componentcarriers that lie in the same frequency band and that are terminated atthe same location (i.e. by one access point). Hence it may be suitableto group certain component carries into timing advance groups where allthe member component carriers of a given group transmit with the sametiming advance specific to this group in the uplink.

When considering for example a state-of-the-art 3GPP communicationssystem setting several timing advances for one user equipment wouldimply that several RACH procedures, one RACH procedure for each timingadvance group, would need to be performed. Thus the eNodeB can determinethe propagation delay for each component carrier group in the uplinkbased the RACH preamble 701, 802 and would then set the appropriatetiming advance for each component carrier group needed using the RandomAccess Response message 702, 802 (see FIG. 7 and FIG. 8). This wouldimply a significant delay caused by executing several RACH proceduresassuming that a user equipment can only perform a single RACH procedureat a time.

Likewise, upon a handover, a user equipment would have to acquire atiming advance value for the component carriers in the target cellthrough RACH procedures, which would mean that there is an increasedinterruption time between the “RRC connection reconfiguration” messageand the “RRC connection reconfiguration completed” message, where UEcannot receive or transmit data. FIG. 10 exemplifies the steps within aconventional non-synchronized handover of a user equipment from a sourceeNodeB to a target eNodeB. After the user equipment receiving a RRCconnection reconfiguration message from the source eNodeB the userequipment acquires downlink synchronization in the target primary cell(PCell) first and performs a random access procedure (RACH procedure)resulting in a time alignment of the uplink component carrier(s) of theprimary cell. Furthermore, in case the user equipment is configured withadditional component carriers by the target eNodeB (in this example,component carriers of two component carrier groups (CoCa Group 1 and 2))that experience different propagation delays then the user equipmentwould need to perform additional RACH procedures (in this example, aRACH procedure of CoCa Group 1 and another RACH procedure of CoCa Group2) that contribute to the handover delay. Upon having time aligned allconfigured uplink carriers, the user equipment finishes thenon-synchronized handover by sending a RRC connection reconfigurationcomplete message.

As highlighted in FIG. 11, in case of a synchronous handover the userequipment would be provided with the timing advance value for theprimary cell of the target eNodeB which would allow avoiding the RACHprocedure for the primary cell (PCell). However, still the RACHprocedures for uplink component carriers of all other timing advancegroups (CoCa Group 1 and 2) would need to be performed to appropriatelyestablish the timing advances for the respective uplink componentcarriers.

Assuming for exemplary purposes that there is an aggregation accesspoint in the network and that there are at least two component carriersthat stem from at least two different physical locations (e.g. due toinvolvement of a remote radio head, RRH), respectively, that areexperiencing different propagation delays (e.g. because the signal pathis through a frequency selective repeater) and further assuming that themobile terminal has at least one uplink component carrier which is timealigned (i.e. the uplink component carrier of the reference cell), themobile terminal can derive the necessary timing advance for thenon-aligned component carrier(s) from one reference timing advance, i.e.the timing advance of the already time aligned uplink component carrierin the reference cell. Furthermore, it should be noted that this is trueas long as the uplink propagation delay is the same as the downlinkpropagation delay for the uplink component carrier and the downlinkcomponent carrier of a given radio cell.

The timing advance for a given non-time aligned uplink component carrierof a radio cell is determined based on the timing advance (for theuplink component carrier) in the reference cell and a reception timedifference or propagation delay difference of transmissions receivingthrough a downlink component carrier of the reference cell and through adownlink component carrier of the radio cell comprising the non-timealigned uplink component carrier.

In the following the procedure for determining the timing advance fornon-timer aligned uplink component carrier according to exemplaryembodiments of the invention will be described with reference to a 3GPPbased system for exemplary purposes only. In the following examples, theaggregation access point is corresponding to an eNodeB, while a furtheraccess point is formed by a Remote Radio Head (RRH) or a FrequencySelective Repeater (FSR).

For exemplary purposes the uplink and downlink component carriers areassumed to have a slotted structure, i.e. transmissions in the uplinkand downlink are transmitted in sub-frames. In the downlink, a sub-framestructure as exemplarily shown in FIG. 3 and FIG. 4 can be used, but theinvention is not limited thereto. Similarly, in the uplink, a sub-framestructure as exemplified in FIG. 3 and FIG. 4 can be used, but theinvention in not limited thereto. The number of subcarriers (i.e. thebandwidth) for an uplink component carrier may be different from thenumber of subcarriers (i.e. the bandwidth) of a downlink componentcarrier. The uplink component carriers may have different bandwidths.Likewise the downlink component carriers may have different bandwidths.

Furthermore, in the uplink, a single sub-frame is assumed to span theentire bandwidth (i.e. all subcarriers (or sub-bands)) of all uplinkcomponent carriers aggregated by an access point (e.g. eNodeB). From theperspective of a user equipment, a single sub-frame is spanning theentire bandwidth (i.e. all subcarriers (or sub-bands)) of all componentcarriers configured by the mobile terminal in the uplink or downlink,respectively. Hence, the data sent within in one sub-frame istransmitted as an individual transmission of modulated symbols (e.g.OFDM symbols) on each component carrier configured in the uplink ordownlink, respectively. Therefore, order to process a given singlesub-frame that is transmitted in the downlink or uplink the mobileterminal (e.g. the user equipment) or the access point (e.g. the basestation or eNodeB) needs to receive all transmissions of the sub-frameon the respective downlink component carriers configured by the mobileterminal, respectively, all uplink component carriers received by the(aggregation) access point (e.g. eNodeB).

FIG. 18 exemplarily shows a sub-frame that is to be transmitted viathree component carriers in the uplink. Assuming for example anOFDM-based communications system, a sub-frame can be defined as a set ofN_(sub-frame) consecutive OFDM symbols (for example 12 or 14 OFDMsymbols) in the time domain and a set of subcarriers corresponding tothe—here three—difference component carriers in the frequency domain.For exemplary purposes, three component carriers CoCa 1, CoCa 2 and CoCa3 are shown that comprise each N_(CoCa1), N_(CoCa2), and N_(CoCa3)subcarriers respectively. The subcarriers of the component carriers mayalso be grouped into individual sub-bands. Further, strictly speaking,the sub-frame does not necessarily span a continuous region ofsubcarriers in the frequency domain; the different subcarriers of thecomponent carriers may also be spaced in the frequency domain.Similarly, the number of the subcarriers of the individual componentcarriers (i.e. their bandwidth) may or may not be the same for thedifferent component carriers. E.g. component carriers CoCa 1 and CoCa 2could be component carriers providing each a bandwidth of 5 MHz, whilecomponent carrier CoCa 3 has a bandwidth of 10 MHz.

The modulation symbols of a respective OFDM symbol that are located onthe subcarriers of a given component carrier are considered atransmission of the sub-frame. Hence, in the example shown in FIG. 18, asingle sub-frame is transmitted by means of three transmissions on thethree component carriers CoCa 1, CoCa 2 and CoCa 3.

In this connection, time alignment of the transmissions on an uplinkcomponent carrier means that the mobile terminal shifts (in time) thesub-frame structure of the respective uplink component carrier relativeto the boundaries of the sub-frames received in the downlink (e.g. thesub-frame boundaries of the downlink component carrier of the referencecell or the radio cell to which the uplink component carrier to betime-aligned belongs). The timing advance (value) indicates the shift intime to be applied relative to the beginning/timing of the sub-frames inthe reference sub-frame structure received in the downlink by the mobileterminal. In case of appropriately configuring the timing advance forthe uplink component carriers (of different radio cells with differentpropagation delays and/or of different mobile terminals) the accesspoint can ensure that the uplink sub-frame boundaries are aligned forall uplink component carriers.

FIG. 19 exemplarily shows the transmission of three consecutivesub-frames (numbered 1, 2 and 3) via three uplink component carriers (asshown in FIG. 18). Due to the user equipment UE using individual timingadvance values for the three component carriers CoCa 1, CoCa 2 and CoCa3, which are assumed to have different propagation delays for exemplarypurposes, the individual transmissions of the respective singlesub-frames become time aligned with respect to their reception at theeNodeB. This facilitates, for example, that the physical layer entity ofthe eNodeB can a single IFFT operation when processing the individualsub-frames.

In one exemplary embodiment of the invention, the timing advance valueTA_(AP2) of a (non-time aligned) uplink component carrier of a radiocell is calculated at the mobile terminal based on the known timingadvance value TA_(AP1) of the (time-aligned) uplink component carrier ofthe reference cell, and further based reception time difference (orpropagation delay difference) ΔT_(prop), as follows:TA_(AP2)=TA_(AP1)+2·ΔT _(prop)  (Equation 1)

The timing advance value TA_(AP1) of the (time-aligned) uplink componentcarrier of the reference cell may have been for example obtained by themobile terminal by performing a RACH procedure as outlined with respectto FIGS. 7 to 9 before, or the timing advance value TA_(AP1) may havealso been calculated earlier by the user equipment as described hereinwith reference to another reference cell.

Furthermore, in one exemplary implementation the time alignment of thereference cell and hence the value of TA_(AP1) may be (constantly)updated by the access point of the reference cell. Hence, in case thetiming advance of the reference cell is updated the mobile terminal mayalso update the timing advance values calculated relative thereto. Theupdate of the timing advance for the uplink component carrier(s) basedon the updated timing advance of the uplink component carrier in thereference cell may also include a new measurement of the reception timedifference (or propagation delay difference) ΔT_(prop) since the thistime difference may also be subject to changes, e.g. due to movement ofthe mobile terminal.

Alternatively, the update of the time alignment of the reference cellmay not cause an update of the timing advance value(s) for the uplinkcomponent carrier(s) of the other radio cell(s). Instead, theaggregation access point (e.g. the eNodeB) could send update commandsfor the timing advance values of the respective uplink componentcarriers or the respective uplink component carrier groups. The updatecommands may for example indicate a correction of the presently settiming advance values. The update commands may be sent for example byMAC control signalling, e.g. within MAC control elements that aremultiplexed to the downlink transmissions.

It is assumed in Equation 1 that the timing advance value TA_(AP2) isdefining the timing advance relative to the reception timing of thedownlink component carrier (or to be more precise relative to thereception timing of the beginning of sub-frames transmitted via thedownlink component carrier) of the radio cell the uplink componentcarrier of which is to be time aligned.

The reception time difference (or propagation delay difference)ΔT_(prop) can be assumed to be defined as:ΔT _(prop) =T _(DL-TCell) −T _(DL-RCell)  (Equation 2)where T_(DL-TCell) denotes the point in time at which the beginning of asub-frame is detected by the mobile terminal within a transmission viathe target cell (TCell), i.e. the radio cell the uplink componentcarrier of which is to be time aligned, and T_(DL-RCell) denotes thepoint in time at which the beginning of the same sub-frame is detectedby the mobile terminal within a transmission via the reference cell(RCell).

In case the timing advance value TA_(AP2) is defining the timing advancerelative to the reception timing of the downlink component carrier ofthe reference cell, the timing advance value TA_(AP2) is calculated asfollows:TA_(AP2)=TA_(AP1) +ΔT _(prop)  (Equation 3)

However, defining the timing advance value TA_(AP2) as in Equation 3 mayhave the disadvantage that in case the reference cell is “dropped”, i.e.the component carrier(s) of the reference cell are deactivated or nolonger configured (e.g. due to handover), the mobile terminal may needto recalculate all timing advance values. This is true in case the lossof the (time alignment in the) reference cell is also implying a loss ofthe time alignment of all other radio cells that are time alignedrelative thereto. However, it may also be the case that after initialtime alignment relative to the reference cells, the time alignment ofthe individual radio cells (i.e. uplink component carriers) isindividually or group-wise updated by the aggregation access point, sothat a loss of the reference cell does not necessarily require a newtime alignment of the other radio cells configured by the mobileterminal.

In the following the determination of the timing advance for non-timealigned uplink component carriers (non-time aligned radio cells) will beoutlined in further detail and reference to some exemplary scenarios. Inthe exemplary scenario shown in FIG. 13, it is assumed that a userequipments aggregates two radio cells, one radio cell originating from afirst location, e.g. an eNodeB, and the other radio cell originatingfrom a different location, e.g. a Remote Radio Head (RRH). A RRH denotesa radio equipment that is connected to and remote to an access point,such as a base station (e.g. a eNodeB in 3GPP based systems) which iscontrolling the RRH. The interface between the access point and the RRHmay be for example use the Common Public Radio Interface (CPRI) standardsee www.cpri.info. The RRH and its controlling access point may be forexample interconnected via a fiber optic cable.

Transmissions via the uplink component carriers of the two radio cellsare processed in the same aggregation node, i.e. the eNodeB in thisexample, and the propagation delay of the downlink component carrier andthe uplink component carrier of each radio cell is the same. The radiocell comprising the uplink component carrier UL CoCa 1 and the downlinkcomponent carrier DL CoCa 1 between the mobile terminal UE and theeNodeB is denoted the primary radio cell (e.g. the PCell of the userequipment), while the radio cell comprising the uplink component carrierUL CoCa 2 and the downlink component carrier DL CoCa 2 between themobile terminal UE and the RRH is denoted secondary radio cell (e.g. aSCell of the user equipment). All transmissions sent from the userequipment via the secondary cell are received by the transceiver of theRRH and a forwarded to the eNodeB via the interface between RRH andeNodeB. Similarly, when transmitting data via the RRH, the eNodeBtransmits the data to the RRH e.g. using CPRI protocols and the RRHforwards the data to the user equipment via the downlink componentcarrier of the secondary cell.

The primary radio cell may be considered to be the PCell of the userequipment in this example and is the reference cell for time alignment.However, also any other radio cell that the user equipment aggregatesand which is currently timing aligned can serve as a reference cell. Forexample, the time alignment of the uplink component carrier UL CoCa1 inthe primary radio cell may have been set by the eNodeB through a RACHprocedure performed in the primary radio cell.

FIG. 15 is showing a procedure according to an exemplary embodiment ofthe invention allowing the user equipment to determine the correct timealignment for non-time aligned uplink component carriers in other radiocells than the reference cell. For exemplary purposes, it is assumedthat the eNodeB is the aggregation access point and that the RRH serversas an additional access point, as outlined with respect to FIG. 13above. The eNodeB transmits sub-frames in the downlink to the userequipment via the primary and secondary radio cell, respectively. Forexemplary purposes, it is assumed that the eNodeB transmits alltransmissions of a single sub-frame (corresponding transmissions)simultaneously. Corresponding transmissions of a given sub-frame areindicated by the same number in FIG. 15. Since the transmissions of agiven sub-frame take different propagation paths, the respectivetransmissions of the given sub-frame are received at different points intime at the user equipment, as highlighted in the upper part of FIG. 15.

The time shift between the transmission of a sub-frame by the eNodeB andthe RRH is for example due to the transmission of the sub-frame via theRRH being forwarded by the eNodeB via the interface to the RRH(propagation delay T_(PD) _(eNB-RRH) ) and from the RRH to the userequipment (propagation delay T_(PD) _(RRH-UE) ). Furthermore, there maybe also a non-neglectable processing delay T_(PROC) _(RRH) of thesub-frames at the RRH, which may need to be taken into account. Thepropagation delay of the transmission of a sub-frame from the eNodeB tothe user equipment via the primary cell is denoted T_(PD) _(eNB-UE) .

The user equipment measures the time difference ΔT_(prop) between thereception of corresponding transmissions of a sub-frame. In more detail,the user equipment determines the difference between the reception timesof a transmission of a sub-frame #i via a downlink component carrier ofthe radio cell in which the uplink component carrier is to be timealigned, and a transmission of the sub-frame #i via a downlink componentcarrier of the reference radio cell. In the example shown in FIG. 15,where the primary radio cell of the eNodeB is the reference cell fortime alignment, the user equipment determines at what point in time thebeginning of a sub-frame transmitted via a downlink component carrier ofthe reference cell is received, and at what point in time the beginningof the of the very same sub-frame via downlink component carrier of theradio cell of the RRH is received, and calculates the time differenceΔT_(prop) of these two reception times.

Time difference ΔT_(prop) between the reception of correspondingtransmissions of a sub-frame assuming a scenario as shown in FIG. 13 isdefined asΔT _(prop)=(T _(PD) _(eNB-RRH) +T _(PROC) _(RRH) +T _(PD) _(RRH-UE) )−T_(PD) _(eNB-UE)   (Equation 4)where the term T_(PROC) _(RRH) may be omitted. Since the eNodeB sendsall transmissions of the sub-frame simultaneously, ΔT_(prop) actuallydenotes the propagation delay difference of the transmission of thesub-frames via the reference cell (primary radio cell) and the secondaryradio cell as shown in FIG. 13.

In order to ensure that corresponding transmissions of a sub-framearrive simultaneously at the eNodeB when sending them through differentuplink component carries experiencing different propagation delays, theuser equipment needs to compensate the measured propagation delaydifference and advance the transmissions further (relative to the uplinktransmission on the uplink component carrier of the reference cell).Hence, in the exemplary scenario of FIG. 13, the transmissions ofsub-frames on uplink component carrier UL CoCa 2 via the RRH is to beadvanced by the reference timing advance TA_(eNodeB) (which is known tothe user equipment) and two times the time difference ΔT_(prop) measuredby the user equipment. Thus the correct timing advance to be applied forthe uplink transmissions of the sub-frames sent via the RRH can becalculated asTA_(RRH)=TA_(eNodeB)+2·ΔT _(prop)  (Equation 5)

As mentioned earlier, the timing advance value TA_(eNodeB) of thereference cell/reference uplink component carrier UL CoCa 1 may havebeen learned by the user equipment from a RACH procedure with the eNodeBor may have been determined in the manner described above based on theknown timing advance from another/previous reference cell.

The eNodeB controlling the reference cell in the scenario of FIG. 13 mayconstantly adjust the time alignment of the uplink component carrier ULCoCa 1 by sending continuous updates of the timing advance valueTA_(eNodeB). The updates of the timing advance may be for example sentvia MAC signalling, e.g. using MAC control elements multiplexed into adownlink transmission sent to the user equipment.

In one further exemplary embodiment of the invention, the time alignmentof an uplink component carrier could be controlled by means of a timer.A separate timer may be maintained by the mobile terminal for eachtiming advance value (each associated to either an individual uplinkcomponent carrier or a uplink component carrier group). The mobileterminal resets and starts the timer each time it receives an updatecommand for a given timing advance value (respectively, plink componentcarrier or a uplink component carrier group). Whenever the timerexpires, i.e. timing alignment is considered to be lost, time alignmentcan be reestablished by the mobile terminal using the mechanismsdescribed herein, e.g. the mobile terminal can recalculate the timingadvance value based on the reference cell and a new measurement of thereception time difference (or propagation delay difference) or the userequipment could alternatively perform a RACH procedure to reestablishtime alignment.

Thus an uplink—in practice—can be considered to be timing aligned aslong as the user equipment maintains a reference timing alignment onanother radio cell's uplink.

As exemplified in FIG. 16, the timing advance value TA_(RRH) may also becalculated relative to the reception timing of the downlink sub-frameboundaries on a downlink component carrier with the reference cell, i.e.downlink component carrier DL CoCa 1 of the primary radio cell as shownin FIG. 13. Accordingly, the equation for calculating the timing advancevalue TA_(RRH) for the uplink component carrier UL CoCa 2 in thesecondary radio cell would be changed to:TA_(RRH)=TA_(eNodeB) +ΔT _(prop)  (Equation 6)where the values TA_(eNodeB) and ΔT_(prop) remain unchanged incomparison to Equation 5.

Furthermore, in the examples of FIG. 15 and FIG. 16, the timing advancevalues TA_(RRH) and TA_(eNodeB) have been chosen to not only align theuplink transmissions on the uplink component carriers with respect tothe sub-frame boundaries, but also to aligned the sub-frame boundariesin the uplink and downlink component carriers. However, this is notmandatory.

As exemplified in FIG. 17, the timing advance values for the uplinkcomponent carriers may be also chosen so that the sub-frame boundariesin the uplink and downlink component carriers are not aligned. This maybe for example achieved in case the reference timing advance value(denoted TA_(AP1) or TA_(eNodeB) in the examples above) is configured bythe aggregation access point (e.g. eNodeB) so as to not correspond totwo times the propagation delay between the aggregation access point andthe mobile terminal, as for example shown in FIG. 9. The timing advancevalues for non-aligned uplink component carrier(s) may be then stilldetermined as outlined above with respect to FIGS. 15 and 16 based onthis reference timing advance value. However, the timing advancevalue(s) calculated on such reference timing advance value will thenstill align the sub-frame boundaries on the uplink component carriers,but not the sub-frame boundaries of uplink and downlink componentcarriers.

The same assumptions and calculations that are described above may alsobe used in scenarios where the over-the-air signal between mobileterminal and aggregation access point, and vice versa, is passingthrough a Frequency Selective Repeater (FSR). A FSR may also be referredto as a bi-directional amplifier (BDA). The FSR is an apparatus thatused for boosting the radio signals of a wireless system in a local areaby receiving the radio signal by means of a reception antenna,amplifying the received radio signal with a signal amplifier andbroadcasting the amplified radio signal via an internal antenna. Theoperation of the FSR is commonly transparent to the other network nodes,i.e. the access points and mobile terminals. The FSR may be assumed toboost the radio signals of one or more component carriers in thedownlink and uplink. In case only a subset of the configured componentcarriers is amplified by a FSR, the radio signals of the differentcomponent carriers may experience different propagation delays, similarto the situation discussed previously herein with respect to FIG. 13.

One difference between the usage of a RRH or a FSR is the location ofreception of the physical layer. Physical layer reception of the uplinktransmissions for the radio cells that originate at the location of theaggregation access point (e.g. eNodeB) takes place at the aggregationaccess point, while for the radio cells originating from the location ofthe RRH for physical layer reception takes place at the RRH. Inherently,the method of time alignment described above for the scenario shown inFIG. 13 adjusts the uplink timing for the radio cells being received atthe RRH in manner that all uplink transmissions of all mobile terminalarrive at the same time at the RRH, which is important forinterference-free reception of all uplink radio signals arriving fromall mobile terminals at the RRH. Furthermore, since processing delay inthe RRH and propagation delay from RRH to aggregation access point (e.g.eNodeB) can be assumed to be the same for all uplink radio signalsreceived at the RRH, all uplink data forwarded by the RRH arrive at theaggregation access point at the same time as well, which is beneficialfor further processing in higher layers.

For the case that a Frequency Selective Repeater is used, all uplinkradio signals are received at the location of the aggregation accesspoint (e.g. the eNodeB). Hence, the physical radio signals of all uplinktransmissions for all radio cells should advantageously arrive at thesame time instance, in order to ensure interference-free physical layerprocessing.

FIG. 14 exemplifies a scenario, where a FSR is used to boost thedownlink and uplink component carriers (DL/UL CoCa 2) of a secondaryradio cell, while the radio signals of the downlink and uplink componentcarriers (DL/UL CoCa 1) of a primary radio cell are not amplified by theFSR. In this scenario it is assumed that the uplink and downlinkcomponent carriers of the secondary radio cell are boosted by the FSRand that the user equipment is not receiving the uplink and downlinkcarriers of the secondary radio cell from the directly eNodeB. Hence, inthis scenario it can be again assumed that the propagation delay ofuplink and downlink component carriers within the secondary radio cellis different from the propagation delay of uplink and downlink componentcarriers within the primary radio cell. Furthermore, there is nopropagation delay difference between the uplink and downlink componentcarriers within the secondary radio cell.

In case it is further assumed that the timing advance value TA_(eNodeB)for the uplink component carrier UL CoCa 1 in the primary radio cell isknown, the user equipment can time align the transmissions on the uplinkcomponent carrier UL CoCa 2 in the secondary radio cell based on thisreference time alignment TA_(eNodeB) and the reception time difference(or propagation delay difference) between the downlink component carriertransmissions in the primary and secondary radio cells in a mannerdescribed above. Basically the same equations above can be reused, wherereplacing the term TA_(RRH) with the term TA_(FSR) denoting the timingadvance value for the uplink component carrier UL CoCa 2 in thesecondary radio cell.

Since the utilization of a FSR may not be known to the mobileterminal—as it is operating in a transparent fashion—the aggregationaccess point (e.g. eNodeB) may inform the mobile terminal(s) whether it(they) are allowed to calculate timing advance values based on areference cell or not. The aggregation access point (e.g. eNodeB) may beaware of the network configuration and thus also about the use andconfiguration of FSR(s) in its vicinity.

Configuration of Timing Advance method by Aggregation Access Point

As already indicated above the mobile terminal (e.g. user equipment) maybe unaware of the location the different radio cells it is aggregatingare stemming from. Hence, in this case, the mobile terminal is alsounaware of the actual propagation delay it's uplink transmissionsexperience. Since mobile terminal may also not know whether both uplinkand downlink of a radio cell are transmitted from the same location, inone further embodiment of the invention the methods for time aligningthe uplink component carriers depending on a reference cell may forexample be applied only in case the aggregation access point isauthorizing this procedure. For example, in a 3GPP based mobilecommunications system, only the eNodeB knows if the user equipment'suplink transmissions experience the same propagation delay as thedownlink signals received by the user equipment, since network topologyand exact location of nodes (access points) and location of transmissionand reception antennas is known to eNodeB.

Taking the above into account for each cell that is configured in themobile terminal (e.g. user equipment), the aggregation access point(e.g. eNodeB) for example signal the uplink time alignment configurationmode, i.e. whether the calculation of timing advance as discussedpreviously herein can be applied for an uplink component carrier oruplink component carrier group, or whether initial timing advance for anuplink component carrier or uplink component carrier group is to be setthrough the RACH procedure.

The signalling can be for example achieved by introducing a flagindicating whether the RACH procedure is to be used for to get timealigned or whether the mobile terminal can calculate the timing advancebased on the reference timing advance. The flag may be signalled foreach individual radio cell or for a group of radio cells the componentcarriers of which experience an equal propagation delay.

The information on how to time align an uplink component carrier of agiven radio cell should be available to the mobile terminal beforetransmission and reception on the radio cell can start. Therefore, inone exemplary implementation, the flag to signal the time alignmentconfiguration mode may be conveyed to the mobile terminal via RRCsignalling when the radio cells are configured. For example, thesignalling information of the flag (e.g. one bit) to indicate the timealignment configuration mode may be for example included in aRadioresource Configuration Message of the RRC protocol.

Synchronized and Non-Synchronized Handover

The methods described above are also usable in a handover scenario,where the mobile terminal is to aggregate new uplink component carriersin one or more target cells. Instead of performing RACH procedure for atarget radio cell, the mobile terminal can determine the uplink timealignment of the uplink component carriers relative to a reference cellcontrolled by the target aggregation node (or base station/eNodeB).

Once reference timing advance has been established in a target radiocell, further radio cells that are configured from the targetaggregation access point (e.g. eNodeB) for the mobile terminal (e.g.user equipment) can be time aligned without using further RACHprocedures. Hence, a handover where mobile terminal shall retain severalaggregated radio cells under control of the target aggregation accesspoint will commence by using only a single RACH procedure for the caseof a non-synchronized handover instead of using one RACH procedure forevery timing advance to be set for the radio cells in the new targetaggregation access point.

The time alignment of the new reference cell under control of the targetaggregation access point can be either obtained trough a RACH procedure(for non-synchronized handover), as mentioned above, or by configuringthe timing advance value for one of the target radio cells through thesource aggregation access point (i.e. the access point, e.g. eNodeB,from which the mobile terminal is handed over to the new/target accesspoint) when using a synchronized handover. In the latter case no RACHprocedure may be required at all in the target cells.

In one exemplary embodiment of the invention referring to a 3GPP basedmobile communications network, such as 3GPP LTE-A, the source eNodeB(serving as an aggregation access point) is initiating the handover bysending a RRC connection reconfiguration message to the user equipment,which is instructing the user equipment to perform a handover. The RRCconnection reconfiguration message informs the user equipment on the neweNodeB (serving as the new aggregation access point) controlling thetarget radio cells which are to be configured by the user equipment.Furthermore, the RRC connection reconfiguration message indicates theradio cells to be configured by the user equipment. Optionally, i.e. incase of a synchronized handover, the RRC connection reconfigurationmessage also comprises a timing advance value for setting the timingadvance for an uplink component carrier (or uplink component carriergroup) under control of the target eNodeB.

In case of a non-synchronized handover, the user equipment establishesdownlink synchronization in the target radio cells and performs a RACHprocedure on one of the uplink component carriers to establish timealignment for this the uplink component carrier (or the uplink componentcarrier group to which the uplink component carrier belongs). Once thetime alignment is established, i.e. a timing advance value is set, theother uplink component carriers configured by the user equipment may betime aligned by the methods outlined herein above. Hence, in case of anon-synchronized handover, the user equipment only needs to perform onesingle RACH procedure, but can time align all uplink component carriers.

In case the eNodeB does not allow for calculating the timing advancevalues based on a reference cell (e.g. by means of RRC controlsignaling), the user equipment may need to perform more than one RACHprocedure to time align uplink component carriers for which the timingadvance value may not be configured based on the timing advance in areference cell. For example, the RRC connection reconfiguration messagecould indicate for which target radio cells the user equipment maycalculate the timing advance based on a reference cell.

In case of a synchronized handover no RACH procedure at all is needed.An initial reference timing advance for a target radio cell serving asthe reference is provided to the user equipment by the source eNodeB.All remaining radio cells controlled by the target eNodeB can then betime aligned using the methods described above (e.g. in case the eNodeBallow the time align the respective radio cell based on a referencetiming advance). As shown in FIG. 12, the handover delay is minimized.The user equipment establishes downlink synchronization in one of thetarget cells (which will service as the reference cell) and configuresthe timing advance as provided by the eNodeB in the RRC connectionreconfiguration message. Then the user equipment only needs calculatethe timing advance values for the other uplink component carrier(s) orcomponent carrier groups, and can then send the RRC connectionreconfiguration complete message back to the new eNodeB to finish thehandover.

Hence, the calculation of the timing advance(s) for the time alignmentof uplink component carriers relative to a reference cell maysignificantly reduce the handover delay and thus reducing the latencyand delay associated with this procedure when compared to the prior artmethods for both, synchronized and non-synchronized handover.

Another aspect of the invention is to time-align a non-time-aligneduplink of a serving cell and to transmit timing information used fortime-aligning the non-time-aligned uplink of the serving cell to theaggregation access point.

The following specific scenario is assumed, however should not beunderstood as limiting the invention, but as an example for describingthe invention's principles. It is assumed that the reference cell is thePCell, and the target cell is the SCell. The aggregation access point isassumed to be the eNodeB.

FIG. 23 discloses a signaling diagram illustrating the various stepsperformed by the mobile terminal UE and the eNodeB, and the messagesexchanged between them to allow the time-alignment procedure accordingto one embodiment of the invention.

The mobile terminal UE has configured a PCell over which it exchangesdata with the eNodeB. The PCell of the mobile terminal UE is alreadytime-aligned in the uplink, i.e. the uplink transmissions made by themobile terminal UE over the PCell are performed by the mobile terminalUE at a timing such that their reception at the eNodeB is synchronizedwith the receptions of uplink transmissions of other mobile terminals UEon this cell. The PCell was uplink-time-aligned initially by performinga RACH procedure as explained in the background section, be itcontention based or non-contention based (see FIGS. 7 and 8).

Though it seems less advantageous, it would be theoretically possible toinitially synchronize the PCell using the principles of the presentinvention, assuming that the reference is an uplink-time-aligned SCell.The following description, however, assumes that the PCell is initiallysynchronized in the uplink using the RACH procedure, since the PCellwill always be uplink synchronized for the case that the UE aggregatesmultiple serving cells, e.g. PUCCH is transmitted on PCell, and willhave the “best” uplink-time-alignment (due to the RACH procedure beingmore accurate).

The mobile terminal UE is now configured with a Secondary Cell, SCell,which however is not yet time-aligned in the uplink. For instance, theSCell has just been configured, or the SCell, having been previouslyuplink-time-aligned, has lost its uplink synchronization (e.g. timingadvance timer expires). In any case, the mobile terminal UE has now toachieve uplink time alignment in order to be able to transmit uplinkdata to the eNodeB through the SCell. The following steps are performedas exemplified by FIG. 23.

1. The mobile terminal UE performs measurements to determine specifictiming information of transmissions/receptions in the PCell and/orSCell. There is various timing information which can be determined atthe mobile terminal UE, as will be explained in detail further below.The timing information which the terminal measures is such that itallows the terminal to determine the timing advance for the SCell byconsidering the uplink time alignment of the PCell, which is alreadytime-aligned and thus serves as a reference for the time-alignment ofthe SCell.

With regard to steps 4 a, 4 b or 4 c, it is important to note that theinformation of the measurements, which may be transmitted to the eNodeB,is such that it isn't already known in the eNodeB, thus, relating totimings which are unknown in the eNodeB, such as to transmission and/orreception timing information of signal exchange performed on the PCelland/or SCell between the mobile terminal UE and the eNodeB.

2. The mobile terminal UE uses the information of the measurement todetermine a timing advance for the SCell. The determination is based onthe information of the measurement and on information referring to theuplink time alignment of the PCell. There are various possibilities howto achieve this, and the following description will discuss them in moredetail.

This timing advance for the SCell will be preferably determined by themobile terminal UE as an absolute value, i.e. similar to the initialtiming advance value known from the standard, which is applied by themobile terminal UE with respect to the time of arrival of a downlinktransmission from the eNodeB on the SCell. Alternatively, the determinedtiming advance may also be relative to the timing advance used for thePCell, thus allowing the mobile terminal UE to apply the value withrespect to the time of transmission of an uplink transmission by themobile terminal UE to the eNodeB on the time-aligned PCell, or withrespect to the time of arrival of a downlink transmission from theeNodeB on the PCell.

With regard to steps 4 a, 4 b or 4 c, the timing advance determined bythe mobile terminal UE for uplink transmissions on the SCell is also notknown by the eNodeB except for the case when the mobile terminal UEperforms a RACH procedure on the SCell or receives a TA command to beapplied for uplink transmissions on the SCell.

In theory, the eNodeB could determine a timing advance by measuring arelative time difference between of uplink transmissions on the PCelland on the SCell, once uplink transmission are performed on the PCelland SCell. However, such measurements would require that UE istransmitting with the wrong timing advance on the SCell creatinginterference with other uplink transmissions on the same SCell. Suchinterference shall, in general, be avoided. Apart from the unbearableinterference, the measurement would not be very precise. In other words,even though there exists a theoretical possibility for the eNodeB tomeasure a timing advance for use by the mobile terminal UE, the timedifference measurements, in practice, do not allow for an exactdetermination of the timing advance on the SCell.

In contrast thereto, a time alignment based on a random access procedureavoid the interference with other uplink transmissions on the SCell. Itshould be noted that the RACH preamble has some specific characteristicsas explained in the background section in order to allow some gooddetection at the eNodeB side.

In other words, even though there exists a theoretical possibility forthe eNodeB to measure a timing advance for use by the mobile terminalUE, the time difference measurements, in practice, do not allow for anexact determination of the timing advance on the SCell.

However, with the mobile terminal providing the information of themeasurements to the eNodeB (as in step 1), the eNodeB can calculate atiming advance for the SCell similar to that determined by the mobileterminal UE in step 2. It will be later explained that the transmittedinformation of the measurements and/or the timing advance for the SCellenable the eNodeB to controlling the time-aligning process in the SCell.For now it is important to note that the eNodeB can also determine atiming advance for the SCell similarly to the mobile terminal UE, namelybased on the information of the measurement and on information referringto the uplink time alignment of the PCell.

3. Using the determined timing advance for the SCell, the mobileterminal UE can time-align the uplink transmission timing of the SCell.How exactly the uplink transmission timing is adjusted depends on theparticular type of the determined timing advance. In case the determinedtiming advance information is an absolute value of the timing advance tobe applied, the mobile terminal UE sets its uplink transmission timingrelative to the beginning of the downlink subframes received over theSCell by the amount of time indicated in the timing advance informationAlternatively, in case the timing advance is determined by the mobileterminal UE relative to the timing advance of the PCell, the mobileterminal UE sets its uplink transmission timing relative to thebeginning of the uplink subframes transmitted over the time-alignedPCell by the amount of time indicated in the time advance information,or relative to a downlink transmission on the PCell.

Thus, the mobile terminal UE time-aligns its uplink of the SCell, andcan then start transmitting scheduled uplink transmissions based onreceived uplink grant.

4 a, 4 b or 4 c. The mobile terminal UE transmits the information on themeasurement of step 1 and/or the timing advance of step 2 to the eNodeBto enable the eNodeB to better control the timing alignment of theSCell.

Transmitting information of the measurements and/or the determinedtiming advance is not necessarily performed after the mobile terminal UEapplying the determined timing advance for time-aligning uplinktransmission on the SCell (i.e. as step 4 c). Alternatively, the mobileterminal UE may transmit the information on the measurement of step 1 tothe eNodeB directly after the measurement thereof in step 1 (i.e. step 4a in FIG. 23) or after the determination step 2 (i.e. step 4 b) or aftertime-alignment of the uplink transmissions on the SCell in step 3 (i.e.step 4 c). According to another alternative, the mobile terminal maytransmit the determined timing advance of step 2 to the eNodeB directlyafter the determination thereof in step 2 (i.e. step 4 b in FIG. 23) orafter time-aligning the uplink transmission on the SCell of step 3 (i.e.step 4 c). In general the timing of the reporting of the timingmeasurements performed by the mobile terminal can be manifold asexplained later: either periodically or event-triggered or requested byeNodeB.

As explained earlier, the eNodeB can also determine, based on thetransmitted information of the measurement in step 4 a, a similar timingadvance for the SCell to that determined by the mobile terminal UE instep 2. With the eNodeB capable of converting between both transmittedinformation, the above described alternative may be considered equalalternatives with respect to the transmitted information.

There are various advantages provided by the present invention asexplained above. First, a procedure is implemented to apply differenttiming advances on different component carriers, i.e. cells. Therefore,in situations where the propagation of the SCell is different to thePCell, the uplink timing can be adjusted for each cell separately whenpossible. Further, performing a random access procedure in the SCell maybe avoided. Further, the prevention of RACH procedures circumventsseveral problems, such as complicated prioritization rules for the powerlimitation, or problems with the power amplifier.

Additionally, the uplink synchronization process for the presentinvention is faster compared to where a RACH procedure is performed. Aswill be shown later in detail this is, in particular, important for theactivation of an uplink non time-aligned SCell. Furthermore, thetransmission, to the eNodeB, of the information of the measurementand/or of a timing advance value for the SCell enables the eNodeB totrack changes in the timing advance of the SCell and the eNodeB tocontrol time aligning uplink transmissions on the SCell in the mobilecommunication system.

In the following a more specific embodiment of the invention will beexplained with reference to FIGS. 24 and 25.

FIG. 24 shows a scenario in which a PCell, SCell1 and SCell2 are servedby the eNodeB to different UEs, namely UE1, UE2, UE3. A FrequencySelective Repeater (FSR) is provided, being configured for thefrequencies used by SCell1 and SCell2, such that it amplifies signalstransmitted/received on the secondary serving cells SCell1 and SCell2,however not those signals transmitted/received on the PCell. Asillustrated by FIG. 24, the coverage of the PCell is greater than theone of the SCells.

In the lower part of FIG. 24 the downlink reception time difference atthe mobile terminal between the SCells1 or 2 and the PCell(Δ_(Scell-PCell)Rx_(DL)) is plotted against the position of a UE in thecell. The downlink reception time difference is the difference betweenthe point in time when the UE receives a downlink subframe from theeNodeB over the SCell and a point in time when the UE receives adownlink subframe from the eNodeB over the PCell.

In this particular scenario, the need for different uplink timingadvances for PCell, SCell1 and SCell2 changes depending on the locationof the UE. In more detail, three UEs are depicted in FIG. 24; UE1 islocated at A, within the coverage of PCell, SCell1 and SCell2; UE2 islocated at B, at the overlapping area of the coverage for SCell1/SCell2provided by the eNodeB and the coverage for SCell1/SCell2 provided bythe FSR; UE3 is located at C, outside coverage for SCell1/SCell2provided by eNodeB, but inside the coverage for SCell1/SCell2 providedby the FSR.

From location A to location B, the PCell, SCell1 and SCell2 are providedby the same transmission node, e.g. eNodeB to the UEs. Therefore, thepropagation delays for the three cells should be substantially the same,and thus the downlink reception time difference should be negligible. Asa result, the same timing advance can be used for the PCell, SCell1 andSCell2. On the other hand, at location B it is assumed that the signalfor SCell1/SCell2 from FSR is stronger than the one for SCell1/SCell2from eNodeB, and correspondingly, the UE2 at location B receives signalsover PCell from the eNodeB and signals over SCell1/SCell2 from the FSR.Consequently, the propagation between PCell signals and SCell1/SCell2signals is different, which results in different downlink receptiontimings between PCell and SCell1/SCell2. As apparent from the lower partof FIG. 24, the plotted downlink reception time difference measured bythe UE2 between PCell and SCell1/SCell2 suddenly jumps to a particularvalue, at the moment when UE2 switches from one reception path (fromeNodeB) to another (from FSR).

At location B the downlink reception time difference is at its maximumsince the path length difference between the PCell path and theSCell1/SCell2 path is at its maximum too in this exemplary scenario. Thedownlink reception time difference decreases as the UE moves furthertowards the FSR, and is minimum directly at the FSR, the downlinkreception time difference mainly being the time of the FSR forreceiving, processing and transmitting the amplified signal forSCell1/SCell2. When moving away again from the FSR, the downlinkreception time difference increases again.

Accordingly, UE2 and UE3 cannot use the same timing advance forSCell1/SCell2 as used for the PCell, but would have to configureseparate uplink timing advances for them. However, the same timingadvance could be used for SCell1 and SCell2, since in the presentscenario the propagation delays for SCell1 and SCell2 are the same.

One of the main ideas of the invention is to determine the timingadvance for the SCell relative to the uplink timing of theuplink-time-aligned PCell. In particular, the timing advance used by UE3to synchronize the uplink transmissions in the SCell is defined inrelation to the uplink timing of the uplink-time-aligned PCell. Thefollowing timing relations apply for a timing advance for the SCell,TA_(SCell), in relation to the timing advance of the PCell, TA_(PCell),and other parameters.

$\begin{matrix}{{{TA}_{PCell} = {{PD}_{UL\_ PCell} + {PD}_{DL\_ PCell}}}\begin{matrix}{{TA}_{SCell} = {{PD}_{UL\_ SCell} + {PD}_{DL\_ SCell}}} \\{= {{PD}_{UL\_ PCell} + {PD}_{DL\_ PCell} + \left( {{\Delta_{{SCell} - {PCell}}{PD}_{DL}} + {\Delta_{{SCell} - {PCell}}{PD}_{UL}}} \right)}} \\{= {{TA}_{PCell} + \left( {{\Delta_{{SCell} - {PCell}}{PD}_{DL}} + {\Delta_{{SCell} - {PCell}}{PD}_{UL}}} \right)}}\end{matrix}} & \left( {{equation}\mspace{14mu} 7} \right)\end{matrix}$wherein Δ_(SCell-PCell)PD_(DL) is the difference between the propagationdelays in the downlink of the PCell and the SCell; and whereinΔ_(SCell-PCell)PD_(UL) is the difference between the propagation delaysin the uplink of the PCell and the SCell.The following substitution:Δ_(SCell-PCell)PD_(UL)=Δ_(SCell-PCell)PD_(DL)+Δ_(SCell)PD_(UL-DL)  (equation8)where Δ_(SCell)PD_(UL-DL) is the difference between the propagationdelays of the uplink and downlink for the SCell, leads to the equation:TA_(SCell)=TA_(PCell)+2·Δ_(SCell-PCell)PD_(DL)−Δ_(SCell)PD_(UL-DL)  (equation9)The following substitution:Δ_(SCell-PCell)PD_(DL)=Δ_(SCell-PCell)Rx_(DL)−Δ_(SCell-PCell)Tx_(DL)  (equation10)where Δ_(SCell-PCell)Tx_(DL) is the downlink reception time differencebetween the PCell and the SCell, i.e. the difference in time between thereception in the UE3 of a downlink transmission from the eNodeB on thePCell and the reception in the UE3 of a downlink transmission from theeNodeB on the SCell, andwhere Δ_(SCell-PCell)Tx_(DL) is the downlink transmission timedifference between the PCell and the SCell, i.e. the difference in timebetween the transmission in the eNodeB of a downlink transmission to UE3on the PCell and the transmission in the eNodeB of a downlinktransmission to UE3 on the SCell, leads to the equation:

$\begin{matrix}\begin{matrix}{{TA}_{SCell} = {{TA}_{PCell} + {2 \cdot \left( {{\Delta_{{SCell} - {PCell}}{Rx}_{DL}} - {\Delta_{{SCell} - {PCell}}{Tx}_{DL}}} \right)} - {\Delta_{SCell}{PD}_{{UL} - {DL}}}}} \\{= {{TA}_{PCell} + {{2 \cdot \Delta_{{SCell} - {PCell}}}{Rx}_{DL}} - {{2 \cdot \Delta_{{SCell} - {PCell}}}{Tx}_{DL}} - {\Delta_{SCell}{{PD}_{{UL} - {DL}}\left( {{equation}\mspace{14mu} 12} \right)}}}}\end{matrix} & \left( {{equation}\mspace{14mu} 11} \right)\end{matrix}$Put differently, the timing advance of the SCell can be calculated basedon:

-   -   the timing advance of the PCell    -   the downlink reception time difference between the PCell and the        SCell    -   the downlink transmission time difference between the PCell and        the SCell    -   the propagation delay difference between the uplink and the        downlink on the SCell

The timing advance of the PCell is basically both known to the eNodeBand UE3.

The downlink reception time difference between the PCell and the SCell(Δ_(SCell-PCell)Rx_(DL)) is not known in the eNodeB, but can be measuredat UE side.

The downlink transmission time difference between the PCell and theSCell Δ_(SCell-PCell)Tx_(DL) is known only by the eNodeB, however not toUE3, as will become more clear in connection with FIG. 27. In theparticular embodiment of FIG. 26, the downlink transmission timedifference between the PCell and the SCell (Δ_(SCell-PCell)Tx_(DL)) iszero; for the embodiment of FIG. 27 explained later the downlinktransmission time difference between the PCell and the SCell(Δ_(SCell-PCell)Tx_(DL)) is not zero.

In relation to the examples of FIGS. 15, 16 and 17, the definition ofthe timing advance TA_(SCell) of equation 11 and equation 12additionally considers the downlink transmission time difference betweenthe PCell and the SCell (Δ_(SCell-PCell)Tx_(DL)) and the propagationdelay difference between the uplink and the downlink on the SCell(Δ_(SCell)PD_(UL-DL)) and is, hence, more precise. In other words, in amobile communication system configured to operate without a transmissiontime difference between the PCell and the SCell(Δ_(SCell-PCell)Tx_(DL)=0) and without a propagation delay differencebetween the uplink and the downlink on the SCell(Δ_(SCell)PD_(UL-DL)=0), as considered with respect to FIG. 26, theequation 12 corresponds to that of the examples of FIGS. 15, 16 and 17.

The propagation delay difference between the uplink and the downlink ofa serving cell, SCell, is assumed to be negligible for the purposes ofthe invention. More specifically, it is assumed that the propagationdelay for the uplink and downlink direction is the same for eachcarrier. Simulation done by 3GPP WG RAN4 provided results of thesimulated propagation delay differences for inter-band carrieraggregation case which show that for the same reception node (i.e. theeNodeB), propagation timing difference will be less than one TA step(˜0.5 us) in 97˜98% case and less than five TA steps in 100% case.Following this for the SIB-2 linked DL and UL carrier pairs, where thefrequency gap between uplink and downlink will be even smaller than thatbetween different frequency bands, resulting in that the propagationtiming difference between the UL direction and the DL direction for agiven cell will be even less and, hence, negligible for the presentinvention.

Assuming the above and considering that the mobile terminal UE shallcalculate a timing advance of the SCell, the mobile terminal UE mayapproximate the timing advance for uplink transmissions on the SCell, asdefined by equation 13 below, namely based on the timing advance of thePCell (TA_(PCell)) and the downlink reception time difference betweenthe PCell and the SCell (Δ_(SCell-PCell)Rx_(DL)). In case of a mobilecommunication system as exemplified in FIG. 27 having different uplinktiming advances for PCell and SCell1/SCell2, it has to be noted thatthe, by the mobile terminal, determined timing advance only approximatesan accurate timing advance for the SCell1/SCell2.

In future releases, a mobile terminal UE may perform uplinktransmissions to plural different eNodeBs at a same time i.e.cooperative multi-point (COMP) transmissions in the uplink. Since twodifferent eNodeBs are not required to use a same downlink timing, thetransmission time difference between a first eNodeB1 providing a PCelland a second eNodeB2 providing a SCell (Δ_(SCell-PCell)Tx_(DL)) needs tobe considered when time aligning uplink transmissions on an SCell.Without this value, a mobile terminal can also only approximate thetiming advance for uplink transmissions on the SCell

Consequently, based on the information of measurements performed by themobile terminal and/or the uplink time alignment for the SCelldetermined by the mobile terminal, only the eNodeB can ensure anaccurate time alignment of uplink transmissions performed by the mobileterminal on the SCell. In other words, transmitting this timinginformation by the mobile terminal to the eNodeB enables the eNodeB toaccurately control the time alignment process for an SCell at the mobileterminal, e.g. in case of cooperative multi-point (COMP) transmissions.

Resulting from the above considerations, a more detailed embodiment ofthe invention for uplink-time-alignment of SCell for UE3 will bepresented below with reference to FIG. 25.

In step 1 of FIG. 25, the UE3 measures the downlink reception timedifference Δ_(SCell-PCell)Rx_(DL) and in particular the time differencebetween the time when the UE3 receives the start of one subframe fromthe PCell and the time when the UE3 receives the corresponding start ofone subframe from the SCell that is closest in time to the subframereceived from the PCell. Correspondingly, UE3 performs the measurementsfor each of the two SCells, resulting in Δ_(SCell-PCell)Rx_(DL) andΔ_(SCell2-PCell)RX_(DL). In the present scenario the downlink receptiontime difference will be substantially the same for SCell1 and SCell2.The downlink reception time difference for one SCell can be seen in FIG.26.

In step 2, the UE3 uses the measurements results to calculate the timingadvance for the SCells. Since the downlink reception time difference isthe same for both SCells, the UE3 will only calculate one timing advancethat may be used by the UE3 to uplink-time-align both SCells.Considering the assumptions of the present embodiment, equation 12discussed above can be written in a simplified manner as:TA_(SCell)=TA_(PCell)+2·Δ_(SCell-PCell)Rx_(DL)  (equation 13)since both Δ_(SCell-PCell)Tx_(DL) and Δ_(SCell)PD_(UL-Dl) may beconsidered zero.

The mobile terminal thus uses the received downlink reception timedifference(s) Δ_(SCell1-PCell)Rx_(DL)/Δ_(SCell)Rx_(DL) and the knowntime advance for the PCell to calculate the time advance for the SCell1and SCell2 TA_(SCell1/SCell2) according to equation 13.

In step 4 b of FIG. 25, the UE3 transmits the results of themeasurements, i.e. the downlink reception time differenceΔ_(SCell1-PCell)Rx_(DL) and/or Δ_(SCell2-PCell)Rx_(DL) and/or thecalculated timing advances for the SCells TA_(SCell1/SCell2) to theeNodeB, preferably by using the PUSCH of the PCell. Alternatively, sinceboth downlink reception time differences are the same, the UE3 maytransmit only one of the two measurements and/or one of the calculatedtiming advances.

In step 3, the UE3 applies the calculated timing advanceTA_(SCell1/SCell2) relative to the beginning of the downlink radio frameof the SCell1 and SCell2, similar to the way in which a standard initialtiming advance is applied by a UE.

In this way, the UE3 can uplink-time-align the SCell1 and SCell2, andstart uplink transmissions thereon according to received uplinkscheduling grants. The first uplink grant is usually part of the RARmessage within the standard RACH procedure. Since in the invention noRACH procedure is performed on an SCell, the first uplink grant for theSCells can be transmitted at any time in any way to the UE3 via thePDCCH.

The UE3 uses an uplink grant on SCell1 and SCell2 to transmit an uplinktransmission to the eNodeB. This is illustrated in FIG. 25 for oneSCell. The UE3 sets the time of transmission of an uplink radio framefor the SCell T_(UL) _(_) _(TX) _(_) _(SCell) relative to the time ofreception of a downlink radio frame for the SCell T_(DL) _(_) _(RX) _(_)_(SCell), by “shifting” by the timing advance value T_(SCell1/SCell2).

Such a time-aligned uplink transmission on the SCell is received atT_(UL) _(_) _(RX) _(_) _(SCell) in the eNodeB, after the propagationdelay PD_(UL) _(_) _(SCell).

Having received in step 4 b from the UE3 information on the downlinkreception time difference Δ_(SCell1-PCell)Rx_(DL) and/orΔ_(SCell2-PCel1)Rx_(DL) and/or the calculated timing advances for theSCells TA_(SCell1/SCell2), the eNodeB is enabled to control timealignment of uplink transmissions on the SCells (step 7).

In particular, as described before, the UE3 transmits the downlinkreception time difference and/or the calculated timing advance to theeNodeB and provides the eNodeB with information it cannot measure orderive by itself. Based on the received information on the downlinkreception time difference Δ_(SCell1-PCell)Rx_(DL) and/orΔ_(SCell2-PCell)RX_(DL) and/or the calculated timing advances for theSCells TA_(SCell1/SCell2), the eNodeB can determine if the time advanceto be used with the SCells allows for accurately time aligned uplinktransmissions by the UE3 on the SCells.

Exemplary, for determining if the received timing advances for theSCells TA_(SCell/SCell2) (which is calculated by the UE3 in step 2)allows for a sufficient time alignment of uplink transmission on theSCells, the eNodeB can compare the received value with a timing advancevalue for the SCells it determines based on the three values: the timingadvance of the PCell, the downlink reception time difference between thePCell and the SCell and the downlink transmission time differencebetween the PCell and the SCell according to equation 12. In case thedifference between the received and the determined timing advance for anSCell is larger than a threshold, the eNodeB determines that the timingadvance to be used with the SCells does not allow for accurately timealigned uplink transmissions by the UE3 on the SCells.

This exemplary determination of whether the timing advance calculated bythe UE3 is sufficient for time aligning uplink transmissions on theSCell can be made before actual uplink transmissions are performed bythe UE3 on the SCell.

Alternatively, for determining if the received timing advances for theSCells TA_(SCell1/SCell2) (which is calculated by the UE3 in step 2)allows for an accurate time alignment of uplink transmission on theSCells, the eNodeB can determine, based on its knowledge of thedeployment of the radio cells of the mobile communication system, if theby the UE3 measured downlink reception time difference between the PCelland the SCell appears correct or not, and based on a thresholddistinguish if the received timing advance is sufficient for timealigning uplink transmissions by the UE3 on the SCells. Thisdetermination of whether the timing advance calculated by the UE3 issufficient for time aligning uplink transmissions on the SCell can alsoin this case be made before actual uplink transmissions are performed bythe UE3 on the SCell.

Furthermore, other exemplary implementations for the eNodeB to determinewhether the timing advance calculated by the UE3 is sufficient for timealigning uplink transmissions on the SCells depend on the mobileterminal performing actual uplink transmission on the SCells havingapplied the calculated timing advance for the SCells TA_(SCell1/SCell2)(of step 2). In case of uplink transmissions by the mobile terminal onthe SCells, the eNodeB may compare a reception time of uplinktransmissions on the uplink of the SCells with a predefined referencetime for uplink transmission on the uplink of the SCells, or compare areception time of uplink transmissions on the uplink of the SCells witha transmission time of downlink transmissions on the correspondingdownlink of the SCells.

In case the eNodeB determines in step 7, that the calculated timingadvance for the SCells TA_(SCell/SCell2) does not allow for accuratelytime-aligned uplink transmissions by the UE3, the eNodeB transmits instep 8 information, instructing the UE3, that the calculated andtransmitted timing advance TA_(SCell1/SCell2) cannot be used by the UE3for time aligning the uplink transmissions on the SCells i.e. that itdoes not allow for accurately time-aligned uplink transmissions on theSCells.

According to one example, the information may include a RACH ordertriggering the mobile terminal, upon reception of the RACH ordermessage, to perform a random access procedure on at least one of theSCells (step 9). As part of the random access procedure, the UE3receives an accurate timing advance for the SCell(s) and time-aligns theSCell(s) by adjusting a timing for uplink transmissions on the uplinktarget cell based on the received timing advance within the randomaccess procedure.

According to another example, the information may include a timingadvance command with a timing advance for use with the SCell triggeringthe mobile terminal, upon reception of the timing advance, to time-alignthe uplink SCell(s) by adjusting a timing for uplink transmissions onthe uplink target cell based on the received timing advance (step 9).

According to further example, the information may include a timingadvance update command triggering the mobile terminal, upon reception ofthe timing advance update command, to determine a timing advance for usewith the uplink of the SCell(s) based on the included target timingadvance update value and on the timing advance used for uplinktransmissions on the uplink of the SCell(s), and the SCell(s) byadjusting a timing for uplink transmissions on the uplink target cellbased on the determined timing advance (step 9).

FIG. 27 illustrates a timing diagram according to another embodiment ofthe invention. Compared to the timing diagram of FIG. 26, the differenceis that the PCell and the SCell perform a downlink transmission atdifferent times, i.e. the downlink subframe timing is not synchronizedbetween Pcell and SCell. Furthermore, it is assumed that the SCell1 andSCell2 have the same downlink transmission timing. In other words, thereis a downlink transmission time difference between the PCell and theSCell Δ_(SCell-PCell)Tx_(DL) which is not zero but is the same forSCell1 and SCell2.

The uplink-time-alignment procedure, explained before in connection withFIG. 25, can be similarly applied to the scenario exemplified in FIG.27, considering the following changes in procedure.

The UE3 can measure the downlink reception time differencesΔ_(SCell1-PCell)Rx_(DL) and/or Δ_(SCell2-PCell)Rx_(DL), which are thesame for SCell1 and SCell2 (step 1 in FIG. 25). It should be noted thatthe downlink reception time difference not only considers thepropagation delay differences between PCell and SCell (as in FIG. 26),but in this case also the downlink transmission time differenceΔ_(SCell-PCell)Tx_(DL).

In this particular embodiment of the invention, the measured downlinkreception time difference Δ_(SCell-PCell)Rx_(DL) is longer than thedifference of the propagation delays between PCell and SCell, i.e.longer by the downlink transmission time difference between the PCelland the SCell Δ_(SCell-PCell)Tx_(DL).

However, since the downlink transmission time difference between thePCell and the SCell Δ_(SCell-PCell)Tx_(DL) is unknown, i.e. transparent,to the UE3, it will calculate timing advance for uplink transmissions onthe SCell based on equation 13 (step 2 in FIG. 25). In particular, theUE3 will assume that the timing advance can be determined based on thetiming advance of the PCell (TA_(PCell)) and the downlink reception timedifference between the PCell and the SCell (Δ_(SCell-PCell)Rx_(DL)).

Exemplary, the UE3 then transmits the results of the measurements, i.e.the downlink reception time difference Δ_(SCell-PCell)Rx_(DL) and/or thecalculated timing advances for the SCell TA_(SCell) to the eNodeB,preferably by using the PUSCH of the PCell (step 4 a in FIG. 25).

Receiving this value, the eNodeB can compare by subtraction the valuewith a timing advance value for the SCell it determines based on thethree values: the timing advance of the PCell, the downlink receptiontime difference between the PCell and the SCell and the downlinktransmission time difference between the PCell and the SCell. Since the,from the UE3 received value does not account for the downlinktransmission time difference between the PCell and the SCell(Δ_(SCell-PCell)Tx_(DL)), the difference is larger than a threshold.

Hence, the eNodeB can determine that the by the UE3 calculated timingadvance for use with the SCells does not allow for accuratelytime-aligned uplink transmissions on the SCells (step 7 in FIG. 25) andthen uses the following equation 14 for alignment of uplinktransmissions by the UE3 on the SCells. Namely, only Δ_(SCell)PD_(UL-DL)is set to zero for the reasons explained before.TA_(SCell)=TA_(PCell)+2·Δ_(SCell-PCell)Rx_(DL)−2·Δ_(SCell-PCell)Tx_(DL)  (equation14)

Exemplary, the eNodeB transmits the determined timing advance TA_(SCell)to the UE3 according to step 8, illustrated in FIG. 25. Accordingly, theUE3 uses the received timing advance value TA_(SCell) for time aligningthe uplink transmissions on the SCell1 and SCell2 with respect to thebeginning of the downlink radio frames on the respective SCell1 andSCell2 (step 9 in FIG. 25). Alternatively, the eNodeB transmits a RACHorder or a timing advance update command as explained earlier.

It should be noted that even though the eNodeB knows the timing advanceused by the UE for uplink transmission on PCell, the UE autonomouschange of the uplink timing according to TS36.133 section 7.1.2 causessome deviation from the timing advance value of the PCell signalled bythe eNodeB to the UE, except only just after the PRACH transmission tookplace. Therefore, according to another alternative embodiment the UEalso reports the used difference between DL radio frames received on thePCell and UL radio frames transmitted on the PCell to the eNodeB inaddition to the downlink reception time difference measurements.

FIG. 28 discloses a flowchart diagram illustrating the various stepsperformed by the mobile terminal UE to allow for time-aligned uplinktransmissions in line with the time-alignment procedure according to anexemplary embodiment of the invention.

It should be noted that in the time-alignment procedure according tothis exemplary embodiment of the invention, the eNodeB respectivelyaggregation access point is the node that controls the uplink timingused by the mobile terminal for transmission on the uplink of the cells.Even though the mobile terminal may calculate autonomously the timingadvance for a target cell (e.g. SCell or group of SCells), theaggregation access point can at any time override this self-calculatedtiming advance and direct the mobile terminal to use another timingadvance that has been determined and signalled by the aggregation accesspoint. The mobile terminal will in this case use the timing advancesignalled from the aggregation access point. Put in other words, thetiming advance signalled by the aggregation access point takesprecedence over the timing advance calculated autonomously by the mobileterminal.

In the following, variants and additional steps for the above-describedembodiments will be presented with reference to FIG. 28.

Triggering of the Step of Reporting by the UE

In the previous embodiments it has been left open when the UE starts themeasurements (step 1 a) and the reporting of the measurement resultsand/or of the calculated timing advance (step 1 c). Measurements may befor example performed periodically.

The reporting/signalling can be performed either periodically orevent-triggered.

For instance, in step 1) in FIG. 28 the periodical triggering of thereporting may be similar to mobility or power headroom or buffer statusreport reporting. The advantage of periodical reports is that the eNodeBgets with a certain frequency up-to-date information on the measurementresults and/or the calculated timing advance. The eNodeB is thus enabledat periodical intervals to determine if the, by the UE calculated timingadvance is sufficient for time alignment of uplink transmissions on theSCell, and thus can continuously control the timing advance of the UEwhen necessary.

Event-triggered reporting is in step 1) in FIG. 28, however, beneficialtoo and may be necessary in order to allow the eNodeB to react quicklyso as to prevent from e.g. interference due to wrong uplink timealignment. Some events are described in the following.

The configuration of an SCell can be used as a trigger for the UE tostart reporting (step 1 c) of the measurement results and/or of thecalculated timing advance to the eNodeB (step 1 b is optional). Themeasurement and reporting is done according to one exemplary embodimentfor configured and deactivated Scell(s). Providing the measurementresults and/or of the calculated timing advance to the eNodeB everytimea new SCell is configured, has additional benefits (step 1 c).

In more detail, the eNodeB is given the opportunity to check whether adifferent timing advance (multi-TA) is required for the newly configuredSCell. Furthermore and in response thereto, the eNodeB can optionallycalculate an accurate timing advance for the UE to be used with theSCell and optionally signal it to the UE (step 4 in FIG. 28). In otherwords, even though the SCell is deactivated (i.e. not used fortransmission), the UE already knows which timing advance to use for thisSCell.

Thus, when the SCell is activated, the UE can immediately apply thepreviously-received timing advance for the SCell, and already transmitwith the correct uplink time alignment (step 4 a). Therefore, theactivation of an SCell would be faster, for example, when compared tothe approach where RACH needs to be performed on a newly activated SCellso as to achieve uplink synchronization. Essentially, the activationdelay for an SCell, when using the present invention, would be the sameas for Rel-10, where SCells have the same timing advance as the PCell.

Alternatively, the activation of an SCell can be used as a trigger bythe UE to start measurements (step 1 a) and reporting (step 1 c) of themeasurement results and/or of the calculated timing advance (step 1 b isoptional). The advantage of using the activation as a trigger is that,when the eNodeB activates an SCell it also intends to scheduletransmissions on the SCell. In order to determine the correct timingadvance used for the uplink transmissions on the activated SCell, it isbeneficial to provide the eNodeB with up-to-date measurement resultsand/or of the calculated timing advance.

Another option to be used as trigger is that the mobile terminalreceives from the eNodeB a specific request to report the measurementresults and/or of the calculated timing advance to the eNodeB. Thiswould allow the eNodeB to decide case-by-case whether the reporting ofthe measurement results and/or of the calculated timing advance isnecessary or not.

There are several possibilities how to transmit this request from theeNodeB to the mobile terminal. For instance, a flag within the RRCmessages which configure the SCell, e.g. RRC connection reconfigurationmessage, could explicitly request for measurement result reporting.

Or, the activation/deactivation command (MAC CE) as illustrated in FIG.29 could contain a flag which explicitly indicates the need for timinginfo reporting, i.e. the eNodeB explicitly request the mobile terminalto report the measurement results and/or of the calculated timingadvance.

The flag could be signalled by using the free “reserved bit” in theactivation/deactivation MAC control element. Since the activation of analready activated SCell is supported (also referred to as reactivation),the activation/deactivation MAC control element could be sent by theeNodeB at any time for requesting reporting of measurement results,without the need to actually activate or deactivate any of the SCells.

Another possibility would be to re-use the so-called “RACH order”message corresponding to the message 801 in FIG. 8, which is a physicallayer signalling (PDCCH with DCI format 1A). Some predefined codepointsor combination of field codepoints within a RACH order for an SCellcould be used as a request for reporting. For example, a RACH order foran SCell with ra-PreambelIndex set to “000000” (i.e. normally indicatingthat the UE should make a contention-based RACH) could be redefined torequest the reporting. Or, a predefined carrier indicator (CI) codepointfor the case of cross-scheduling can be used as request. The advantagewould be that the uplink resource allocation where the mobile terminalshall transmit the measurement results and/or of the calculated timingadvance can be sent together with the request for measuring and/orreporting, hence reducing the reporting delay.

Another trigger event for reporting (step 1 c) the measurement resultsand/or of the calculated timing advance (step 1 b optional) could bethat the measurement results performed in connection with theuplink-time-alignment of the SCell exceed a certain preconfiguredthreshold.

Such a reporting by the UE is especially beneficial in cases where theeNodeB is not aware of the necessity of using a timing advance for theSCell different to the one of the PCell. The eNodeB may not always havesufficient knowledge from e.g. an OAM (Operation, Administration andMaintenance usually providing cell deployment info like presence ofrepeaters or RRHs).

Also, the need for multi-timing-advance depends on the position of theUE (see FIG. 26 and corresponding description). Thus, e.g. afrequency-selective repeater may be transparent to the eNodeB, and isonly made visible to the eNodeB by the UE reporting on a high downlinkreception time difference. Or even if the eNodeB is aware of the FSR, itdoes not know when exactly the UE will receive the SCell not anymorefrom the eNodeB but via the FSR.

Triggering of the Step of Time-Aligning by the UE

Similarly to the previous embodiments, the mobile terminal UE asillustrated in FIG. 28 measures (step 2 a) the downlink reception timedifference Δ_(SCell-PCell)Rx_(DL) between the SCell and PCell andcalculates (step 2 b) a timing advance TA_(SCell) for uplinktransmissions on the SCell based on the reception time differenceΔ_(SCell-PCell)Rx_(DL) between the SCell and PCell and the timingadvance used for uplink transmissions on the PCell. Then, the mobileterminal UE time-aligns (step 2 c) uplink transmissions on the SCellbased on the calculated timing advance for the uplink SCell.

However, in the previous embodiments, it has always been left open whenthe UE time-aligns uplink transmission on the SCell and how thetiming-alignment is updated for the SCell over time.

The time-alignment for the SCell can be performed either periodically orevent-triggered. In particular, an event-triggered time-alignmentprocedure is advantageous with respect to an initial time-alignment ofuplink transmissions of an SCell. Periodically triggered time-alignmentensures that the uplink-transmissions performed by the mobile terminalUE remain time-aligned even at times when the timing advance of theSCell is not controlled by the eNodeB.

For an event-triggered timing-alignment of uplink-transmissions on theSCell, the same trigger mechanisms as described with respect toevent-triggered reporting can be used. In particular, the UE may beconfigured to use the configuration of an SCell as a trigger forstarting the timing-alignment procedure of the SCell. Alternatively, theactivation of an SCell can be used as a trigger by the UE for startingthe timing-alignment procedure of the SCell. Another alternative fortriggering the timing-alignment procedure of the SCell is when themobile terminal UE receives from the eNodeB a specific messagerequesting the start of the time-alignment procedure of the SCell.

Due to the similarities between the measurements for reporting (step 1a) and the measurements for time-alignment (step 2 a) and thesimilarities between the calculation of the timing advance for reporting(step 1 b) and the calculation of the timing advance for time-alignment(step 2 b), the mobile terminal may, according to another exemplaryimplementation, simultaneously perform the steps for reporting of themeasurements results and/or the calculated timing advance for the SCell(step 1 c) and the steps for time-aligning uplink transmissions on theSCell (step 2 c) and, hence, would only require one event-trigger.

A periodically performed time-alignment procedure is exemplified in FIG.28.

In FIG. 28, the mobile terminal UE ensures that uplink transmissionsremain time-aligned by means of a timer. A separated timer may bemaintained by the mobile terminal for each timing advance value (eachassociated to either an individual uplink cell or a group of uplinkcells).

The mobile terminal resets and starts the timer each time it (i) appliesa calculated timing advance (step 2 d) or (ii) performs a RACH procedure(step 3 c) or (iii) applies a received timing advance value for uplinktransmissions on the respective PCell or SCell for which the timer ismaintained. In this respect, as long as the timer is running, the mobileterminal UE considers itself as being uplink synchronized.

Whenever the timer expires (step 2), i.e. timing alignment is consideredto be lost, the mobile terminal uses the mechanisms described herein toreestablish a time alignment for uplink transmissions on an SCell.

For example, the mobile terminal may use a newly determined timingadvance for the SCell to time-align the uplink transmission timing ofthe SCell (step 2 c).

Upon having reestablished timing alignment for the SCell, the mobileterminal resets and starts the timer (step 2 d) since the mobileterminal UE considers itself as being uplink synchronized.

Determining the Timing Advance for the SCell

As described with reference to FIGS. 26 and 27, the mobile terminal may(re-)establish a time alignment on an SCell by calculating a timingadvance value based on the measured downlink reception time differenceΔ_(SCell-PCell)Rx_(DL) and the timing advance used for uplinktransmissions on the PCell.

Alternatively or in addition, the mobile terminal can measure and reporta reception transmission time difference between the PCell and the SCellΔ_(SCell-PCell)Rx_(DL)−Tx_(UL) and/or a timing advance calculated basedthereon and on the timing advance used for uplink transmissions on thePCell.Δ_(SCell-PCell)Rx_(DL)−Tx_(UL) =T _(DL) _(_) _(RX) _(_) _(SCell) −T_(UL) _(_) _(TX) _(_) _(PCell)as is also depicted in FIG. 26 or 27.

Put into words, the reception transmission time difference between thePCell and SCell is the time difference between the time when the mobileterminal transmits an uplink radio frame on the PCell and the time whenthe mobile terminal receives a downlink radio frame on the SCell. Theuplink radio frame and downlink radio frame shall refer to the sameradio frame number.

As can be seen from either FIG. 26 or 27, the downlink reception timedifference Δ_(SCell-PCell)Rx_(DL) can be calculated based on thereception transmission time difference Δ_(SCell-PCell)Rx_(DL)−Tx_(UL)and the timing advance of the PCell TA_(PCell,) in particular by:Δ_(SCell-PCell)Rx_(DL)=Δ_(SCell-PCell)Rx_(DL)−Tx_(UL)−TA_(PCell)  (equation15)where TA_(PCell) could also be substituted by the time measured betweenT_(UL) _(_) _(TX) _(_) _(PCell) and T_(DL) _(_) _(RX) _(_) _(PCell). Themeasured time between T_(UL) _(_) _(TX) _(_) _(PCell) and T_(DL) _(_)_(RX) _(_) _(PCell) could also be reported to the eNodeB along with thereception transmission time difference.

Measuring and reporting the reception transmission time differenceinstead of or additionally to the downlink reception time difference isbeneficial, since for future techniques like cooperative multi-point(COMP) transmissions in the uplink, the reception transmission timedifference could be used to control the uplink transmission timing.Furthermore, it might be more preferably from the implementation pointof view.

The reception transmission time differenceΔ_(SCell-PCell)Rx_(DL)−Tx_(UL) is then used to calculate the timingadvance for the SCell by the mobile terminal UE and/or reported to theeNodeB, which then also uses equation 15 to calculate the downlinkreception time difference Δ_(SCell-PCell)Rx_(DL). Based on thecalculated downlink reception time difference, the mobile terminaland/or eNodeB can calculate the timing advance for the SCell asexplained before and in more detail later.

It should be noted that the mobile terminal may for example count thenumber of samples as a way of determining the time difference. Forexample, in order to determine the downlink reception time difference,the mobile terminal would count the number of samples between thereception time of a downlink subframe in the PCell and the receptiontime of a downlink subframe in the SCell. For instance, the downlinksubframes may refer to common reference signals (CRS).

Reporting of the Measurement Results

The mobile terminal, after performing the measurements (step 1 a),transmits the results to the eNodeB. As explained before, themeasurements may refer to the downlink reception time differenceΔ_(SCell-PCell)Rx_(DL) and/or to the reception transmission timedifference Δ_(SCell-PCell)Rx_(DL)−Tx_(UL) between the PCell and SCell.(step 1 c)

The reporting itself could be implemented in principle on severallayers, e.g. RRC layer or MAC layer. Other measurements like mobility orpositioning measurements are signaled on the RRC layer too. Since thetiming advance commands are generated by the MAC layer, it could bebeneficial from an implementation point of view, to also implement thereporting of the measurement results on the MAC layer.

FIGS. 29 and 30 illustrate the format of a MAC control element which canbe used to transmit the measurement results from the mobile terminal tothe eNodeB. As apparent, the structure of the MAC CEs is similar to theextended power headroom MAC CE. The size depends on the number ofconfigured or configured and activated SCells, i.e. on the number ofSCells for which measuring and reporting is to be performed.

In more detail, FIG. 29 shows a MAC control element to transmit thedownlink reception time difference between the PCell and all theavailable SCells 1-n.

On the other hand, FIG. 30 illustrates the MAC control element totransmit the reception transmission time difference between the PCelland all the available SCells 1-n. Since the time between T_(UL) _(_)_(TX) _(_) _(PCell) and T_(DL) _(_) _(RX) _(_) _(PCell) corresponds toTA_(PCell), and hence should be actually known by the eNodeB, in analternative embodiment this information must not be reported to theeNodeB.

Instead of reporting the downlink reception time difference and/or thereception transmission time difference for all SCells, the mobileterminal may only report them for the particular SCell which is to betime-aligned.

Further, instead of reporting the downlink reception time differenceand/or the reception transmission time difference for all SCells, themobile terminal may report the calculated timing advance for the SCellto be time-aligned based on the calculated timing advance value asdescribed earlier.

Furthermore, the time differences could be encoded and indicated in thenumber of samples, i.e. the mobile reports a particular number ofsamples, and the eNodeB can then use the number of samples and a sampletime to derive the actual time differences.

As already mentioned previously, the measurement results are preferablytransmitted on the physical uplink shared channel, PUSCH, of the PCell.

Determining the Timing Advance for the SCell

In the previous embodiments of the invention, it was assumed that themobile terminal and/or the eNodeB calculates a timing advance value asknown from the standard RACH procedure, i.e. a timing advance that isapplied by the mobile terminal relative to the beginning of downlinkradio frames received via the downlink SCell, as exemplified in FIGS. 26and 27 (see arrow TA_(SCell)).

This may be termed as an absolute value, since the timing advance valueis of the same type as the timing advance defined by the standard, notto be defined relative to the PCell but relative to the downlinkreception of radio frames in the SCell.

There are however other alternatives too. The timing advance calculatedby the mobile terminal and/or the eNodeB and applied by the mobileterminal UE does not need to be relative to the beginning of downlinkradio frames received via the downlink SCell; other references can bechosen.

For example, the calculated and applied timing advance can be relativeto the beginning of downlink radio frames received via the PCell T_(DL)_(_) _(RX) _(_) _(PCell), or relative to the beginning of uplink radioframes transmitted via the PCell T_(UL) _(_) _(TX) _(_) _(PCell).

In case the timing advance is calculated relative to the beginning ofuplink radio frames transmitted via the PCell, it basically refers tothe difference of the timing advance between the PCell and SCellΔTA_(PCell-SCell).

where considering equation 12:ΔTA_(PCell)=+2·Δ_(SCell-PCell)Rx_(DL)−2·Δ_(SCell-PCell)Tx_(DL)−Δ_(SCell)PD_(UL-DL)

Thus, the timing advance determined by the mobile terminal UE and/oreNodeB is ΔTA_(PCell-SCell).

As described with reference to FIGS. 26 and 27, the mobile terminal doesnot know about the downlink transmission time difference between thePCell and the SCell (Δ_(SCell-PCell)Tx_(DL)) and the propagation delaydifference between the uplink and the downlink on the SCell(Δ_(SCell)PD_(UL-DL)) and, hence, determines the timing advanceΔTA_(PCell-SCell) assuming both values Δ_(SCell-PCell)Tx_(DL) andΔ_(SCell)PD_(UL-DL) to be zero.

In contrast, in case the eNodeB determine a timing advanceΔTA_(PCell-SCell), e.g. for checking if the measurement performed by themobile terminal UE allows for a sufficient time alignment of uplinktransmission on the SCell, the eNodeB may determine the timing advanceΔTA_(PCell-SCell) based on its additional knowledge of the downlinktransmission time difference between the PCell and the SCell(Δ_(SCell-PCell)Tx_(DL)) and the propagation delay difference betweenthe uplink and the downlink on the SCell (Δ_(SCell)PD_(UL-DL)).

The mobile terminal in turn applies this value relative to the beginningof uplink radio frames received via the PCell, to determine the uplinktiming for uplink transmissions performed on the SCell. This isexemplified in FIG. 31, where the timing advance is indicated by thenumber of samples N_(TA), and is then multiplied with the sample timeT_(S) to acquire the actual difference in time to apply for uplinktransmissions in the SCell compared to the uplink transmissions in thePCell.

In case the timing advance is calculated relative to the beginning ofdownlink radio frames received via the downlink PCell, the timingadvance value isTA_(SCell)+Δ_(SCell-PCell)Rx_(DL)as can be deduced from FIG. 26 and FIG. 27.

Thus, the mobile terminal first derives the current timing advance valueTA_(SCell) and subtracts therefrom the downlink reception timedifference Δ_(SCell-PCell)Rx_(DL).

The calculation result is used to set the timing of uplink transmissionson the SCell based on the received timing advance relative to thebeginning of the downlink radio frame received by the mobile terminal inthe PCell.

This is exemplified in FIG. 32, where the timing advance is indicated bythe number of samples N_(TA), and is then multiplied with the sampletime T_(S) to acquire the actual difference in time to apply for uplinktransmissions in the SCell.

Reception of a Random Access Channel, RACH, Order

As described with respect to the previous embodiments, the mobileterminal transmits timing information to the eNodeB, enabling the eNodeBto control the time-aligning process for the uplink of an SCell or groupof SCells.

In connection with FIG. 25, it has been described that the eNodeB maydetermine, upon reception of measurement results and/or a calculatedtiming advance from the mobile terminal, if the transmitted informationallows for an accurate time alignment of uplink transmissions on theSCell (e.g. in case of a non-zero downlink transmission time differencebetween the PCell and the SCell).

Alternatively, the eNodeB may also determine (i.e. without reference tothe received timing information) that the time-alignment of the PCellused by the mobile terminal UE does not allow for an accurate timealignment of uplink transmissions on the SCell.

For example, when the eNodeB detects that the time-alignment of uplinktransmission by the mobile terminal on the PCell is not accurate, theeNodeB may according to an example, immediately transmit a random accesschannel, RACH, order message to the mobile terminal UE. In other words,in case the mobile terminal would use a timing advance for the SCellwhich was, for example, based on a borderline timing advance of theuplink of the PCell, the eNodeB can prevent from interference betweenuplink transmissions on the SCell by immediately transmitting a RACHorder message to the mobile terminal. Errors in a timing advance ofuplink transmissions on the PCell (i.e. reference cell) propagate to thecalculated timing advance for uplink transmissions on the SCell to-betime-aligned.

As another example, the configuration of the PCell and the SCell mayalso trigger the eNodeB to immediately transmit a random access channel,RACH, order message to the mobile terminal UE. Based on particularconfigurations of the PCell and the SCell, the eNodeB may assume thatthe calculation of a timing advance for an SCell by the mobile terminaldoes not allow for an accurate time alignment of uplink transmissions onthe SCell. For instance, if the PCell and the SCell are configured onwidely separated frequency bands, the eNodeB may determine that themobile terminal cannot calculate an accurate timing advance for theSCell.

Should the eNodeB determines that the mobile terminal UE is not able tocalculate a timing advance which would accurately time-align uplinktransmission on the SCell, the eNodeB may, in one example, immediatelytransmit a random access channel, RACH, order message to the mobileterminal. In other words with the RACH order message the eNodeB ensuresa robust time-alignment of uplink transmissions on the SCell and avoidsan un-controllable uplink timing advance drift.

The RACH order message preferably corresponds to message 801 in FIG. 8,which is a physical layer signalling (PDCCH with DCI format 1A).

In step 3 in FIG. 28, when the mobile terminal receives a RACH ordermessage, the mobile terminal performs a random access procedure asdescribed with reference to FIG. 8.

As part of the random access procedure (i.e. step 802), the mobileterminal receives an accurate timing advance for the SCell. The mobileterminal then time-aligns the SCell by setting a time advance for uplinktransmissions on the uplink target cell based on the timing advancereceived within the random access procedure (step 3 b in FIG. 28).

Thereafter, the mobile terminal resets and restarts the respectivetiming advance timer for the SCell or group of SCells on which therandom access procedure has been performed (step 3 c in FIG. 28).

Reception of a Timing Advance Command

Another alternative for the eNodeB to control the time-aligning processuplink for the uplink of an SCell or group of SCells is the transmissionof a timing advance command.

As described with respect to the previous embodiments, the mobileterminal UE transmit timing information to the eNodeB, enabling theeNodeB to calculate a timing advance for uplink transmissions on aparticular SCell or group of SCells in a similar manner to thecalculation of the timing advance by the mobile terminal.

In some situations, as described earlier, only the eNodeB is able tocalculate a timing advance which allows for an accurate time alignmentof uplink transmissions on the particular SCell or group of SCells (e.g.in case of a non-zero downlink transmission time difference between thePCell and the SCell).

In such a situation, the calculated timing advance can be transmitted tothe mobile terminal e.g. using the downlink shared channel of the SCellto which the timing advance shall be applied.

FIG. 33 shows the format of a timing advance command to be used fortransmitting the calculated timing advance from the eNodeB to the mobileterminal, according to one particular embodiment of the invention. Ifthe timing advance information calculated and transmitted to the mobileterminal is the TA_(SCell) (and not some of the relative valuesmentioned above in connection with FIGS. 31 and 32), 11 bits arepreferably used to transmit the timing advance for the SCell to achievethe necessary granularity (same as for the initial TA command known fromthe standard).

On the other hand, less bits suffice if the timing advance is smaller,due to being relative to another timing.

One example is using a new MAC control element to convey the timingadvance information with e.g. 8 bits. Alternatively, the timing advanceupdate command, known from Release 8 of LTE, can be used, having aformat as shown in FIG. 33. One of the free R-bits could be used todistinguish between an actual timing advance update command as knownfrom the standard, and the timing advance information according to oneof the various embodiments of the invention.

Since some embodiments use a relative timing advance (see description inconnection with FIGS. 31 and 32), the six bits provided by the timingadvance update command may provide sufficient granularity.

Another alternative would be that the eNodeB sends timing advanceinformation not only for one SCell but for all configured respectivelyconfigured and activated SCells. In case the UE reports timinginformation for all configured respectively configured and activatedSCells according to a previous embodiment, it could make sense to alsoreport all the calculated TA in response.

In step 4 in FIG. 28, when the mobile terminal UE receives a timingadvance command from the eNodeB using the downlink shared channel of aSCell or of one of group of SCells to which the timing advance shall beapplied, the mobile terminal UE time aligns uplink transmissions usingthe conveyed timing advance value on the SCell or group of SCells (step4 a of FIG. 28).

Thereafter, the mobile terminal resets and restarts the respectivetiming advance timer for the SCell or group of SCells on which the timeadvance has been applied (step 4 b in FIG. 28).

Grouping of SCells

In the scenario assumed for FIGS. 24, 25 and 26, SCell1 and SCell2 havethe same timing advance in the uplink since the propagation delay forSCell1 and SCell2 is the same. In said case, the SCell1 and SCell2 canbe said to form a timing advance group.

Further to this scenario, there may be several respectively configuredand activated SCells, forming different timing advance groups, dependingon whether the SCells can be uplink-time-aligned using the same timingadvance value. As already explained, there are several reasons leadingto the need for different timing advances between various SCells of asame mobile terminal. An example is one or more frequency-selectiverepeater, amplifying the signals of only some of the SCells.

In any case, if the mobile terminal stores a mapping of SCells tospecific timing advance groups, when having to time-align an SCell1,belonging to a timing advance group with a time-aligned SCell2, themobile terminal can immediately apply the timing advance previously usedfor the time-aligned SCell2, to time-align the uplink transmissions ofSCell1 too. Thus, there would be no need to perform all the steps of theinvention.

The mapping of SCells to timing advance groups can be configured andupdated by the eNodeB only.

Hardware and Software Implementation of the Invention

Another embodiment of the invention relates to the implementation of theabove described various embodiments using hardware and software. In thisconnection the invention provides a user equipment (mobile terminal) anda eNodeB (base station). The user equipment is adapted to perform themethods described herein. Furthermore, the eNodeB comprises means thatenable the eNodeB to determine the power status of respective userequipments from the power status information received from the userequipments and to consider the power status of the different userequipments in the scheduling of the different user equipments by itsscheduler.

It is further recognized that the various embodiments of the inventionmay be implemented or performed using computing devices (processors). Acomputing device or processor may for example be general purposeprocessors, digital signal processors (DSP), application specificintegrated circuits (ASIC), field programmable gate arrays (FPGA) orother programmable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments of the invention may individually or in arbitrarycombination be subject matter to another invention.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

The invention claimed is:
 1. A method for time aligning uplinktransmissions by a mobile terminal in a mobile communication system, themobile terminal being in communication with an aggregation access point,the method comprising the steps of: configuring the mobile terminalsimultaneously with a time-aligned uplink reference cell and with anon-time-aligned uplink target cell, both cells being controlled by theaggregation access point, measuring, by the mobile terminal,transmission and/or reception time difference information relating totransmissions on the target cell and/or reference cell, determining, bythe mobile terminal, a first target timing advance based on at least themeasured transmission and/or reception time difference information andon a reference timing advance used for uplink transmissions on thetime-aligned reference cell, time-aligning, by the mobile terminal, theuplink target cell by adjusting a timing for uplink transmissions on theuplink target cell based on the determined first target timing advance,and transmitting the measurement results and/or the first target timingadvance from the mobile terminal to the aggregation access point.
 2. Themethod according to claim 1, wherein, based on a timer included in themobile terminal, the steps of (i) measuring the transmission and/orreception time difference information, (ii) determining the first targettiming advance, (iii) time-aligning the uplink target cell, and (iv)transmitting the measurement results and/or the first target timingadvance, are repeated by the mobile terminal, unless otherwiseinstructed by the aggregation access point.
 3. The method according toclaim 1, wherein the step of measuring by the mobile terminal comprises:determining by the mobile terminal a downlink reception time difference(delta Scell-PCellRX.sub.DL) between the target and reference cell, bymeasuring the time between the beginning of a first downlink subframe onthe target cell (T.sub.DL_RX_SCell) and the beginning of thecorresponding downlink subframe on the reference cell(T.sub.DL_RX_PCell), wherein downlink subframes on the reference andtarget cell refer to the same subframe number, and optionally whereinthe measurement results, transmitted to the aggregation access point,comprise the downlink reception time difference between the target andreference cell.
 4. The method according to claim 1, wherein the step ofmeasuring by the mobile terminal further comprises: determining by themobile terminal a reception transmission time difference between thetarget and reference cell (delta Scell-PCellRX.sub.DL-Tx.sub.UL), bymeasuring the time difference between the time when the mobile terminaltransmits an uplink radio frame on the reference cell(T.sub.UL_TX_PCell) and the time when the mobile terminal receives adownlink radio frame on the target cell (T.sub.DL_RX_SCell), wherein theuplink radio frame and the downlink radio frame relate to the same radioframe, and optionally wherein the measurement results, transmitted tothe aggregation access point, comprise the reception transmission timedifference between the target and reference cell.
 5. The methodaccording to claim 4, wherein the step of determining the first targettiming advance at the mobile terminal further comprises the step of:determining a downlink reception time difference between the target celland the reference cell (delta.sub.Scell-PcellRx.subDL) by subtractingthe reception transmission time difference from the timing advance ofthe reference cell.
 6. The method according to claim 1, wherein the stepof time-aligning the target cell comprises setting the transmission ofuplink radio frames on the uplink target cell relative to the beginningof downlink radio frames received via the downlink target cell, usingthe first target timing advance determined considering that the settingof the transmission of the uplink radio frames on the uplink target cellwill be relative to the beginning of downlink radio frames received viathe downlink target cell, respectively, or setting the transmission ofuplink radio frames on the uplink target cell relative to the beginningof downlink radio frames received via the downlink reference cell, usingthe first target timing advance determined considering that the settingof the transmission of the uplink radio frames on the uplink target cellwill be relative to the beginning of downlink radio frames received viathe downlink reference cell, or setting the transmission of uplink radioframes on the uplink target cell relative to the beginning of uplinkradio frames transmitted via the uplink reference cell, using the firsttarget timing advance determined considering that the setting of thetransmission of the uplink radio frames on the uplink target cell willbe relative to the beginning of uplink radio frames transmitted via theuplink reference cell.
 7. The method according to claim 1, wherein themeasurement results are transmitted to the aggregation access point onthe physical uplink shared channel, PUSCH, of the reference cell, and/orwherein the step of transmitting the measurement results is part of theradio resource control layer, RRC, or of the medium access controllayer, MAC, and in case it is part of the MAC layer, the measurementresults are preferably transmitted within a MAC control element.
 8. Themethod according to claim 1, wherein the step of measuring the timedifference information and the step of determining a first target timingadvance by the mobile terminal and of transmitting the measurementresults and/or the first target timing advance to the aggregation accesspoint is: performed periodically, and/or triggered by predeterminedevents, such as: i. configuration and/or activation of the target cellii. the measurement results exceeding a predetermined threshold iii.expiration of a timer iv. reception of a measurement reporting requestfrom the aggregation access point.
 9. A mobile terminal fortiming-aligning uplink transmissions in a mobile communication system,the mobile terminal being in communication with an aggregation accesspoint, the mobile terminal comprising: a processor adapted to measuretransmission and/or reception time difference information relating totransmissions on the target cell and/or reference cell, the mobileterminal being simultaneously configured with a time-aligned uplinkreference cell and with a non-time-aligned uplink target cell, bothcells being controlled by the aggregation access point the mobileterminal, the processor adapted to determine a first target timingadvance based on at least the measured transmission and/or receptiontime difference information and on a reference timing advance used foruplink transmissions on the time-aligned reference cell, the processorand a transmitter adapted to time-align the uplink target cell byadjusting a timing for uplink transmissions on the uplink target cellbased on the determined first target timing advance, and the transmitteradapted to transmit the measurement results and/or the first targettiming advance from the mobile terminal to the aggregation access point.10. The mobile terminal according to claim 9, further comprising a timerand a receiver, and wherein based on the timer, the processor andtransmitter are adapted to repeat measuring the transmission and/orreception time difference information, determining the first targettiming advance, time-aligning the uplink target cell, and transmittingthe measurement results and/or the first target timing advance, unlessthe mobile terminal receives via the receiver an instruction from theaggregation access point instructing the mobile terminal otherwise. 11.The mobile terminal according to claim 9, further comprising a receiver,wherein the processor and transmitter are adapted to measure thetransmission and/or reception time difference information and theprocessor is adapted to determining the first target timing advance incase of the receiver: receiving, from the aggregation access point,information, preferably as a RRC message configuring the target cell,indicating that uplink transmissions on the uplink target cell require adifferent time alignment than that used for the reference cell, orreceiving, from the aggregation access point, information indicating atiming advance group for the target cell which is different from thetiming advance group of the reference cell.
 12. The mobile terminalaccording to claim 9, wherein the processor is adapted to determine adownlink reception time difference (delta.sub.Scell-.sub.PCellRx.sub.DL)between the target and reference cell, by measuring the time between thebeginning of a first downlink subframe on the target cell(T.sub.DL_RX_SCell) and the beginning of the corresponding downlinksubframe on the reference cell (T.sub.DL_RX_PCell), wherein downlinksubframes on the reference and target cell refer to the same subframenumber, and optionally the transmitter is adapted to transmit downlinkreception time difference between the target and reference cell as themeasurement results to the aggregation access point.
 13. The mobileterminal according to claim 9, wherein the processor is adapted todetermine a reception transmission time difference between the targetand reference cell (delta.sub.Scell-PCellRx.sub.DL-Tx.sub.UL) bymeasuring the time difference between the time when the mobile terminaltransmits an uplink radio frame on the reference cell(T.sub.UL_TX_PCell) and the time when the mobile terminal receives adownlink radio frame on the target cell (T.sub.DL_RX_SCell), wherein theuplink radio frame and the downlink radio frame relate to the same radioframe, and optionally the transmitter is adapted to transmit thereception transmission time difference between the target and referencecell as the measurement results to the aggregation access point.
 14. Themobile terminal according to claim 9, wherein the processor is adaptedto determine a downlink reception time difference between the targetcell and the reference cell (delta.sub.Scell-PCellRx.sub.DL) bysubtracting the reception transmission time difference from the timingadvance of the reference cell.
 15. The mobile terminal according toclaim 9, wherein the processor and transmitter are adapted, fortime-aligning the target cell, to set the transmission of uplink radioframes on the uplink target cell relative to the beginning of downlinkradio frames received via the downlink target cell, using the firsttarget timing advance determined considering that the setting of thetransmission of the uplink radio frames on the uplink target cell willbe relative to the beginning of downlink radio frames received via thedownlink target cell, respectively, or wherein the processor andtransmitter are adapted, for time-aligning the target cell, to set thetransmission of uplink radio frames on the uplink target cell relativeto the beginning of downlink radio frames received via the downlinkreference cell, using the first target timing advance determinedconsidering that the setting of the transmission of the uplink radioframes on the uplink target cell will be relative to the beginning ofdownlink radio frames received via the downlink reference cell, orwherein the processor and transmitter are adapted, for time-aligning thetarget cell, to set the transmission of uplink radio frames on theuplink target cell relative to the beginning of uplink radio framestransmitted via the uplink reference cell, using the first target timingadvance determined considering that the setting of the transmission ofthe uplink radio frames on the uplink target cell will be relative tothe beginning of uplink radio frames transmitted via the uplinkreference cell.
 16. The mobile terminal according to claim 9, whereinthe transmitter is adapted to transmit the measurement results to theaggregation access point on the physical uplink shared channel, PUSCH,of the reference cell, and/or wherein the transmitter is adapted totransmit measurement results as part of the radio resource controllayer, RRC, or of the medium access control layer, MAC, and in case itis part of the MAC layer, the measurement results are preferablytransmitted within a MAC control element.
 17. The mobile terminalaccording to claim 9, wherein the processor and the transmitter areadapted to measure the time difference information, to determine a firsttarget timing advance and to transmit the measurement results and/or thefirst target timing advance to the aggregation access point:periodically, and/or upon being triggered by predetermined events, suchas: i. configuration and/or activation of the target cell ii. themeasurement results exceeding a predetermined threshold iii. expirationof a timer iv. reception of a measurement reporting request from theaggregation access point.
 18. The mobile terminal according to claim 9,wherein the receiver is adapted to receive: a deactivation/activationcommand as the measurement reporting request from the aggregation accesspoint for deactivating/activating a configured cell, including a flagindicating the request for measurement reporting, the flag preferablybeing set in one of the reserved bits of the deactivation/activationcommand, or a radio resource control connection reconfiguration messageas the measurement reporting request from the aggregation access point,including a flag indicating the request for measurement reporting, or arandom access channel, RACH, order message as the measurement reportingrequest from the aggregation access point, or a random access channel,RACH, order message as the measurement reporting request from theaggregation access point, with a predetermined codepoint or apredetermined combination of codepoints indicating the request formeasurement reporting.
 19. A non-transitory computer readable mediumstoring instructions that, when executed by a processor of a mobileterminal, cause the mobile terminal to time align uplink transmissionsin a mobile communication system, wherein the mobile terminal: is incommunication with an aggregation access point and simultaneouslyconfigured with a time-aligned uplink reference cell and with anon-time-aligned uplink target cell, both cells being controlled by theaggregation access point, measures transmission and/or reception timedifference information relating to transmissions on the target celland/or reference cell, determines a first target timing advance based onat least the measured transmission and/or reception time differenceinformation and on a reference timing advance used for uplinktransmissions on the time-aligned reference cell, time-aligns the uplinktarget cell by adjusting a timing for uplink transmissions on the uplinktarget cell based on the determined first target timing advance, andtransmits the measurement results and/or the first target timing advancefrom the mobile terminal to the aggregation access point.